The main reason that there is such a limit is to prevent jamming of connections for people that do not have a fast connection. The forum displays images sequentially and by post, so if you have 4 images in 1 post then you end up getting those 4 loaded before the next 4, in theory this is.
You also then get a certain number of posts before a new page is created.
Yes the forum admin control this, personally I think that 4 images per post is fine. If you need to display more images, off site links would be the best suggestion.
Mick
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