You can check by comparing the results in the ewwwio table (Bulk Optimize->Show Optimized Images) with what is served from their CDN. If you can’t tell for sure, let me know, and I’ll take a closer look.
sort of, and yes. From the developer docs at http://developer.wordpress.com/docs/photon/ it looks like the images are fetched on the fly (when they are first viewed, which would obviously be after they are uploaded and optimized). If no resizing/cropping is requested by your blog (look for additional parameters after the image urls when you turn on Photon), then the images should be nearly identical. Photon also runs jpegoptim (pretty much identical to jpegtran) and optipng on all images served.
However, Photon does some other magic with auto-scaling and such that could cause the Photon version to differ from the EWWW version. So, in general, the image sizes should be as good or better when you use Photon. EWWW can give you better PNG optimization (and 2.0 will give you some amazing lossy JPG compression), so the best results will be achieved by using EWWW and Photon together.
