Well as Bill says, you have to have somewhere to put them. The other part with a forum is that you need to provide a means of people getting to them.

In the case of Mudcat, you can provide a link in a thread. Some forums do allow an HTML IMG tag to load an image when the page opens of provide an alternative method to achieve the same thing but that option is not available here (it can slow page downloads down considerably for some users for one thing...)

For the sites that do allow ebmedded images, http://www.imageshack.us/ was recommended on another forum I use the other day as it makes a link for a thumbnail you can copy paste rather than have a big picture (which probably would make you unpopular) embedded in the page.