The userscript helps you find larger images for currently ~6300 hardcoded websites (using ~3700 rules), but it supports a number of generic engines, which means it can in theory work for almost any website.
Some of the websites it supports includes:
Social media websites (incl. Instagram, Patreon, Pinterest, Reddit, Twitter, Tumblr, VK, VSCO, Weibo)
News websites (incl. BBC, Daily Mirror, Huffington Post, The Guardian, The Independent, Vogue)
The script performs a number of functions, all of which can be configured in the options page.
Redirect images opened in their own tabs to larger/original versions
Display a "Hover Zoom"-style popup if Shift+Alt+I (or Ctrl+Shift if you installed prior to 0.8.29) is held when the mouse is over an image (automatic gallery detection, image rotation, and zoom are supported) This is needed for websites like Instagram and VK, where it needs to know the page hosting the image in order to find the larger image
Under the userscript menu, there's a button that will allow you to replace all images on a page to their larger versions. This can be useful if you're using it alongside an extension that will download all images on a page
The pop-up and the preview might take a few seconds to show as it currently needs to download the entire image before being able to display it.
You may encounter a warning from your userscript manager that the script is performing a cross-domain (or cross-origin) request.
The script will request the generated URL before redirecting or previewing, to either ensure it exists, or download the image (if using the pop-up). Cross-domain requests are also used in API calls, such as for Flickr, DeviantArt, and Reddit.
By default, it also checks for updates through Github's API. It does not automatically install any updates, it will only notify you if there is an update when visiting the options page. This can be disabled by disabling "Check Updates" in the options page.
If you want to see exactly what happens, search for do_request in the userscript.
Why does it redirect to a smaller image?
Sometimes websites will scale images up, so this will return the original image. However, if the first image is indeed larger and isn't scaled, please file an issue, and I will fix it ASAP.
Why does it redirect to a scaled-up image?
Most likely because the original image is scaled-up. I try to make sure the script doesn't return any URLs that will scale up an image, but if you believe there's an error, please file an issue.
Yes, it's Apache 2.0 licensed (similar to MIT). Please see the README on github for basic documentation.
An image reloads infinitely when opened in a new tab
This is likely because you have a different userscript/extension that also redirects images. Unfortunately there's not much I can do to automatically improve compatibility, but here are a few things you can do (from least to most invasive):
Add the website hosting the image that redirects infinitely to Image Max URL's blacklist (in the options page)
Disable redirection support for Image Max URL
Disable either the other userscript/extension or Image Max URL
If this is not caused by another extension, please file an issue and I'll try to fix it. There are actually several safeguards in Image Max URL to prevent this from happening, but there can always be bugs.