Works great, recommended for managed WP hosting

I highly recommend using Kraken coupled with the Imsanity plugin, especially if you also use something like Flickr Pick-a-Picture to find and attribute photos while editing posts in WordPress. This way you can reduce the whole process of finding, attributing, and optimizing photos to a few clicks. This is essential on sites with a high, daily posting volume as a convenience for their staff/admin users.

Previously I used EWW Image Optimizer, but the libraries it requires are not supported by the managed hosting I use now (Flywheel) and will often bog down your server if its busy or you’re uploading a batch of photos. Yahoo’s Smush.it service is another free alternative (for now) that can be used through a plugin, but it has big limitations, can be unreliable, and the plugin does not fail gracefully. At its best, smush.it’s results are very inferior to kraken.io’s as well as most desktop image optimization tools.

Initially I was not excited about relying on yet another commercial third party service hooked into WordPress through a plugin, but it beats using a weak, unreliable, non-commercial service. Short of optimizing each image manually in Adobe or GIMP I don’t think you can get better results, and the “hands-free” automation is a real time saver.