FOSS gamedev and creative worlds

The Forum does not display thumbnails of images uploaded in the attachment.
Please add a thumbnail preview of them.

Usually people include the uploaded images directly in the same post. I agree, having thumbnails would be a nice feature but each image would need to be pre-processed from the server (downscale and chop). Caching them would speed up the page load speed but increase the disk usage.
In short: I don't see a big request in this feature yet. Let's see what other people say to this idea.

If I remember correctly, PHPbb does already have that feature. It is also enabled by default. But maybe its broken or it got disabled?

Well such a thumbnail does not realy consume very much disk space. Also disk space is very cheap in today times.