I wonder if Peter / Tim are aware that TM-Img is now changing file extensions. That is a relatively new "feature" (as Microsoft would call it!).
This "feature" was introduced with version 4.0.4 which I installed about a year ago. Unfortunately it was intentional on the part of the developer in order to "standardise" the JPEG file type extension. Since a) the jpg extension is the more common type, and b) in order to support files uploaded before the version 4.0.4 (we are now at V 4.0.10) both .jpg and .jpeg files are supported I can not understand the need to convert the file extensions.
Unfortunately the code is very complex and I have had no success in finding the section where the file name extensions are changed.
I have registered some feedback to the developer.