The image filter module is really neat, but for people reading it is limited to basic functionality like crop and resize. It supports PNG, GIF and JPEG, but PNGs are usually too large and GIFs are low quality, so you are stuck with JPEGs. Not sure if webp support is on the way or not.
There's one serious problem with using 3rd party Imaging SDKs or utilities to build your service on: You're stuck with their flaws and you can't do much about it.
We have written our own image processing SDK, using only encoders which are 3rd party (libpng, libjpeg, libwebp etc), rest is all handwritten, GPU optimized code. The rationale behind it was to be able to tweak/optimize any feature.
