Are you going to allows users to upload images? I was too lazy to register for one of those free sites and I already have one with ImageShack, so I just paid them $40 for a year (lazy, I know), but would be nice to upload images to the forums, unless you're worried about forums space?
Yeah I know, sad. I have my own f-n website and googledrive, but I was legitimately too lazy in that instance to log into the control panel and upload the img and link to it, so you can imagine going to a free site and filling out the register process was totally off limits, and since I had already done everything with imageshack... was just the push of a button. What can say, sometimes complete laziness rules the day.
I'm sorry but that seems... Stupid. There are many free sites that do not require registration (imgur, veuwer, postimg etc) and imageshack is just terrible. Well, whatever I guess.