The UK is probably one of the worst places in the English-speaking world to be accused of hosting something illegal. I've considered hosting a kink social network here (competition with Fetlife), but any sort of image sharing system would leave me incredibly open to the police. I've known people who hosted specific kink-related forums and similar, even without an image upload system, and had huge problems.

As far as I can tell the most reasonable thing to do if I wanted to go through with this would be to develop the software, and sell it on an ongoing basis to a company somewhere with reasonable laws which can actually operate it.