Kraken.io is a freemium web based image optimizer that works by using compression algorithms to condense the file size of images.
The free web interface is capable of compressing images of up to 1MB in size. It comes with three different optimization levels: lossy, lossless, and expert. In most cases the lossy level will provide good results without distorting the image beyond recognition. You can expect a reduced file size anywhere from 20-60%.
Kraken offers a paid version that has API access for developers to integrate into applications. There is also an official WordPress plugin available that can automatically optimize image uploads; as well as optimize images that have already been uploaded. A Magento plugin is also available for Pro. Kraken Pro users can optimize larger images up to 32MB in size.
Real world example: the featured image of this post is 1356×762. Before condensing the image was 193.91 KB. After running it through Kraken it came down to 65.71 KB, or a 66.12% savings. If ever in doubt, you should save the image as both Jpeg and PNG/GIF and then run both of them through Kraken to see which yields the best results.
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