Which way are you posting your screenshots to the forums?

Uploading images to the forum generally works really well. I've been doing it a lot for the No CC Decades Challenge thread and so far no problems. 

However, without spoilers a picture heavy thread is hard to read. The show more feature (instead of pages) means that there is a lot to load when the story gets longer. For the thread mentioned above that is not a huge issue, as I've included links to the different portions of the thread and you can settle for just loading those comments. For a story thread, however, it gets hard to load. For my own story (The Whittaker Saga) I have therefore set up a blog where I write the posts and then just link to that and add a single image in each comment. That way the size is kept down and the one image can help guide readers into 'have I read this or not yet?' territory so they click the right link. 

I hope that helps you in your decision of what is right for you.