I was having trouble attaching pictures too. It was saying that my picture was too big. I ended up copying the picture into Microsoft paint and just shrinking the size of it. (Remember to shrink the size of the white area too.) Then I saved the paint file and attached that. I'm not sure if this is the best way, but it got my picture up.
Are you trying to attach to your post? Or linking from a photo sharing/hosting site? If attaching to your post, it is possible they photos are too big and need to be resized.