We have gone through a lot of image optimization plugins in our day, a lot. They all have their different perks, but none of them gave us the full package until we were introduced to Kraken.
Kraken is a premium plugin that optimizes images at a phenomenal rate. Their site beautifully demonstrates the optimization process, as well as offers a free optimization tool in order to check it out for yourself. I highly recommend it.
After installing the plugin, it’s super easy to use as it will optimize images as they’re being uploaded to your site from that moment forward. If you want to optimize all the images already in your media library, there’s an option for that too. Just go to your media library and select the images you want to optimize, then from the bulk options dropdown choose the “Krak’em All” option.
We loved the plugin so much we wrote our own tutorial on how to use Kraken. It should answer any other questions you may have.