It has come to my attention, that it is possible images can become distorted if they are uploaded incorrectly. For instance, you may see something like this:
This is quite odd, but luckily, there is an easy solution. The reason this has occured is because the image files were uploaded in ASCII format, which is basically a format best used for text based files.
To rectify the problem, re-upload only your forums image files using your FTP client. Before re-uploading them though, set your FTP client to "AUTO" mode - which is when the FTP client chooses the best format to upload an individual file. An example of what to look for is in the image below (note: this was for SmartFTP, it may differ between FTP clients)
You would select "AUTO" (the button the yellow box points to) and proceed to re-upload the image files.