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Published: Oct 1, 2018 License: MIT Imports: 37 Imported by: 0



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imgproxy is a fast and secure standalone server for resizing and converting remote images. The main principles of imgproxy are simplicity, speed, and security.

imgproxy can be used to provide a fast and secure way to replace all the image resizing code of your web application (like calling ImageMagick or GraphicsMagick, or using libraries), while also being able to resize everything on the fly, fast and easy. imgproxy is also indispensable when handling lots of image resizing, especially when images come from a remote source.

imgproxy does one thing — resizing remote images — and does it well. It works great when you need to resize multiple images on the fly to make them match your application design without preparing a ton of cached resized images or re-doing it every time the design changes.

imgproxy is a Go application, ready to be installed and used in any Unix environment — also ready to be containerized using Docker.

See this article for a good intro and all the juicy details! imgproxy: Resize your images instantly and securely

Sponsored by Evil Martians

"No code is better than no code."

imgproxy only includes the must-have features for image processing, fine-tuning and security. Specifically,

  • It would be great to be able to rotate, flip and apply masks to images, but in most of the cases, it is possible — and is much easier — to do that using CSS3.
  • It may be great to have built-in HTTP caching of some kind, but it is way better to use a Content-Delivery Network or a caching proxy server for this, as you will have to do this sooner or later in the production environment.
  • It might be useful to have everything built in — such as HTTPS support — but an easy way to solve that would be just to use a proxying HTTP server such as nginx.

imgproxy uses probably the most efficient image processing library there is, called libvips. It is screaming fast and has a very low memory footprint; with it, we can handle the processing for a massive amount of images on the fly.

imgproxy also uses native Go's net/http routing for the best HTTP networking support.


Massive processing of remote images is a potentially dangerous thing, security-wise. There are many attack vectors, so it is a good idea to consider attack prevention measures first. Here is how imgproxy can help:

  • imgproxy checks image type and "real" dimensions when downloading, so the image will not be fully downloaded if it has an unknown format or the dimensions are too big (there is a setting for that). That is how imgproxy protects you from so called "image bombs" like those described at

  • imgproxy protects image URLs with a signature, so an attacker cannot cause a denial-of-service attack by requesting multiple image resizes.

  • imgproxy supports authorization by an HTTP header. That prevents using imgproxy directly by an attacker but allows to use it through a CDN or a caching server — just by adding a header to a proxy or CDN config.


There are two ways you can install imgproxy:

From the source
  1. First, install libvips.
# macOS
$ brew tap homebrew/science
$ brew install vips

# Ubuntu
# Ubuntu apt repository contains a pretty old version of libvips.
# It's recommended to use PPA with an up to date version.
$ sudo add-apt-repository ppa:dhor/myway
$ sudo apt-get install libvips-dev

Note: Most libvips packages come with WebP support. If you want libvips to support WebP on macOS, you need to install it this way:

$ brew tap homebrew/science
$ brew install vips --with-webp
  1. Next, install imgproxy itself:
$ go get -f -u

imgproxy can (and should) be used as a standalone application inside a Docker container. It is ready to be dockerized, plug and play:

$ docker build -t imgproxy .
$ docker run -e IMGPROXY_KEY=$YOUR_KEY -e IMGPROXY_SALT=$YOUR_SALT -p 8080:8080 -t imgproxy

You can also pull the image from Docker Hub:

$ docker pull darthsim/imgproxy:latest
$ docker run -e IMGPROXY_KEY=$YOUR_KEY -e IMGPROXY_SALT=$YOUR_SALT -p 8080:8080 -t darthsim/imgproxy

imgproxy can be deployed to Heroku with the click of the button:


However, you can do it manually with a few steps:

$ git clone && cd imgproxy
$ heroku create your-application
$ heroku buildpacks:add
$ heroku buildpacks:add
$ git push heroku master


imgproxy is Twelve-Factor-App-ready and can be configured using ENV variables.

URL signature

imgproxy requires all URLs to be signed with a key and salt:

  • IMGPROXY_KEY — (required) hex-encoded key;
  • IMGPROXY_SALT — (required) hex-encoded salt;

You can also specify paths to files with a hex-encoded key and salt (useful in a development environment):

$ imgproxy -keypath /path/to/file/with/key -saltpath /path/to/file/with/salt

If you need a random key/salt pair real fast, you can quickly generate it using, for example, the following snippet:

$ xxd -g 2 -l 64 -p /dev/random | tr -d '\n'
  • IMGPROXY_BIND — TCP address to listen on. Default: :8080;
  • IMGPROXY_READ_TIMEOUT — the maximum duration (in seconds) for reading the entire image request, including the body. Default: 10;
  • IMGPROXY_WRITE_TIMEOUT — the maximum duration (in seconds) for writing the response. Default: 10;
  • IMGPROXY_DOWNLOAD_TIMEOUT — the maximum duration (in seconds) for downloading the source image. Default: 5;
  • IMGPROXY_CONCURRENCY — the maximum number of image requests to be processed simultaneously. Default: double number of CPU cores;
  • IMGPROXY_MAX_CLIENTS — the maximum number of simultaneous active connections. Default: IMGPROXY_CONCURRENCY * 10;
  • IMGPROXY_TTL — duration in seconds sent in Expires and Cache-Control: max-age headers. Default: 3600 (1 hour);
  • IMGPROXY_USE_ETAG — when true, enables using ETag header for the cache control. Default: false;
  • IMGPROXY_LOCAL_FILESYSTEM_ROOT — root of the local filesystem. See Serving local files. Keep empty to disable serving of local files.

imgproxy protects you from so-called image bombs. Here is how you can specify maximum image dimensions and resolution which you consider reasonable:

  • IMGPROXY_MAX_SRC_DIMENSION — the maximum dimensions of the source image, in pixels, for both width and height. Images with larger real size will be rejected. Default: 8192;
  • IMGPROXY_MAX_SRC_RESOLUTION — the maximum resolution of the source image, in megapixels. Images with larger real size will be rejected. Default: 16.8;

You can also specify a secret to enable authorization with the HTTP Authorization header:

  • IMGPROXY_SECRET — the authorization token. If specified, request should contain the Authorization: Bearer %secret% header;

imgproxy doesn't send CORS headers by default. To enable CORS headers, specify allowed origin:

  • IMGPROXY_ALLOW_ORIGIN - when set, enables CORS headers with provided origin. CORS headers are disabled by default.

When you use imgproxy in development, it would be useful to ignore SSL verification:

  • IMGPROXY_IGNORE_SSL_VERIFICATION - when true, disables SSL verification, so imgproxy can be used in development with self-signed SSL certificates.
  • IMGPROXY_QUALITY — quality of the resulting image, percentage. Default: 80;
  • IMGPROXY_GZIP_COMPRESSION — GZip compression level. Default: 5;
  • IMGPROXY_JPEG_PROGRESSIVE — when true, enables progressive compression of JPEG. Default: false;
  • IMGPROXY_PNG_INTERLACED — when true, enables interlaced compression of PNG. Default: false;
  • IMGPROXY_BASE_URL - base URL part which will be added to every requestsd image URL. For example, if base URL is and /path/to/image.png is requested, imgproxy will download the image from Default: blank.

Generating the URL

The URL should contain the signature and resize parameters, like this:

Resizing types

imgproxy supports the following resizing types:

  • fit — resizes the image while keeping aspect ratio to fit given size;
  • fill — resizes the image while keeping aspect ratio to fill given size and cropping projecting parts;
  • crop — crops the image to a given size.
Width and height

Width and height parameters define the size of the resulting image. Depending on the resizing type applied, the dimensions may differ from the requested ones.


When imgproxy needs to cut some parts of the image, it is guided by the gravity. The following values are supported:

  • no — north (top edge);
  • so — south (bottom edge);
  • ea — east (right edge);
  • we — west (left edge);
  • ce — center;
  • sm — smart. libvips detects the most "interesting" section of the image and considers it as the center of the resulting image.

If set to 0, imgproxy will not enlarge the image if it is smaller than the given size. With any other value, imgproxy will enlarge the image.

Encoded URL

The source URL should be encoded with URL-safe Base64. The encoded URL can be split with / for your needs.


Extension specifies the format of the resulting image. At the moment, imgproxy supports only jpg, png and webp, them being the most popular and useful web image formats.


Signature is a URL-safe Base64-encoded HMAC digest of the rest of the path including the leading /. Here's how it is calculated:

  • Take the path after the signature — /%resizing_type/%width/%height/%gravity/%enlarge/%encoded_url.%extension;
  • Add salt to the beginning;
  • Calculate the HMAC digest using SHA256;
  • Encode the result with URL-safe Base64.

You can find helpful code snippets in the examples folder.

Serving local files

imgproxy can process files from your local filesystem. To use this feature do the following:

  1. Set IMGPROXY_LOCAL_FILESYSTEM_ROOT to your images directory path.
  2. Use local:///path/to/image.jpg as the source image url.

Source image formats support

imgproxy supports only the most popular image formats of the moment: PNG, JPEG, GIF and WebP.


There is a special endpoint /health, which returns HTTP Status 200 OK after server successfully starts. This can be used to check container readiness.


Sergey "DarthSim" Aleksandrovich

Many thanks to @romashamin for the awesome logo.


imgproxy is licensed under the MIT license.

See LICENSE for the full license text.


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