Very good

A great image optimizer. Some may argue it’s better to optimize images individually in Photoshop or GIMP or whatever but if you need to keep eager clients on a leash and prevent them from uploading massive unoptimized images this does the trick really well. Original images can be stored alongside optimised versions and the compression levels can be altered per image if needed. If you’re not uploading many images to your site the free quota will suffice (bearing in mind that each uploaded image may count for 3, 4 or more credits depending on how many image sizes you have set up) and one-time extra credits allow for affordable multiple uploads.

I’ve had a few small issues with files type being unrecognised for a few PNG files exported from GIMP, hence only 4 stars (I would have gone with 4.5 if I could), but that said it’s only been with 3 or 4 images out of many hundreds.