One of the common problems with phpbb is that the forum design expands in width when users post images that are too wide for the forum. Here are two fixes to this problem.

There is a fairly advanced mod for phpbb3 that allows you to apply an automatic image resize in forum posts, together with an optional lightbox. You can find it here.

For those of you who are interested in a less advanced solution, here is a little hack that will automatically resize all posted images down to a width of 550px wide.

Preview

With this hack, images that are too large to fit, like this:

are automatically resized in a size that fits, like this one:

Download

Download the file from here.