The biggest problem being... The image being shared is only going to be relevant for a short period of time in 90% of the cases. It massively increases the space consumed by the forum. And so on...
That is why I recommend my forum users to use a third party service (IMGUR is what I recommend) for sharing images.
Of course, I might be in a minority here... Just a suggestion... Offer support for integration with some of the third party image sharing services. IMGUR has an excellent API that can be used here.