Just to give a further update on this question for those who have an interst in technical issues.

I have now located the section of the code which converts the file extension from .jpg to .jpeg. I have also understood the method used.

The background of this is that original versions of windows required a 3 letter extension whereas other operating systems could use a 4 letter file extension. All operating systems now have the capability of using a 4 letter extension however the 3 letter .jpg extension remains the most commonly used.

For the moment I have returned to the original convention. That means that the rare files that are uploaded with a .jpeg extension will be converted to .jpg

Unfortunately the code is quite complex and I have not been able to make it function so that the original file extension, be it .jpg or .jpeg, is retained, the way the code works it must be one or the other.

For the moment any files uploaded with either .jpg or .jpeg extensions will have the .jpg extension which will allow them to be used as an avatar (unless the file size is small I would recommend using the thumbnail).

For the moment this means that a small change will need to be made in the code every time there is an update. I hope that in the future the developer makes a change which allows both extensions to be retained. The question also remains that perhaps UBB.threads (the software used by this forum) should update their code to support both extensions too.