350 pixels is the horizontal maximum for images, but I'm interested in what would be considered the ideal width for character pictures. Most seem to be a lot smaller than that.
Topic on Forum:Page Images
Generally, the pixel size for images is limited by the space available in the content window, so whenever setting images in the edit window, I suggest using the preview function to test different values until an idea size has been determined.
By the way, good thing you fixed the image. I saw that the other pictures on the page used "frame" and got stuck thinking that it must be the way to have nice pictures on the right side of the screen and wondered why it wouldn't rescale. (I haven't dealt with wiki pictures before.) Now the perfectionist in me is just bothered by the presence of the "enlarge" link. It doesn't fit with the rest of the page pictures! Maybe I should upload a smaller version, but the proper size is hard to see when the picture isn't in its correct place...