A Pi3 has a vector processing unit and a fair amount of compute power. However, its not really up to the task of doing intensive image processing, just light weight stuff like affine transforms or transcoding and the like. Heavy weight/real time image processing takes openCL working against a fair number of GPU cores.
You could “stream” images off of a Pi and then do image processing somewhere else.
One other limitation of the Pi architecture is that all the “network” interfaces are basically hanging off of a single USB hub. That means your USB camera, ethernet and even the on board WiFi share the same bandwidth on the USB hub Sadly, this greatly limits the video + networking performance of a Pi. BTW, this is the same architecture as the Pi2. The 3 really didn’t change that much other than the Arm core and speed.