Please see http://en.wikipedia.org/wiki/Wikipedia:Village_pump_(proposals)/Archive_74#Several_changes_to_file_naming - a proposal to fix certain consistency issues with file naming. The main points which cause unnecessary confusion are filenames which vary solely in the file extension, but are of the same file type: File:X.jpg, File:X.jpeg, File:X.JPG should all refer to the same file, but currently do not.
a. Multiple filetype extensions for the same filetype: As it stands, two
separate users could upload two separate images of two separate subjects as
File:TestImage.jpg and File:TestImage.jpeg. There is no reason for this.
b. Case sensitivity in filetype extensions: As it stands, and as does happen, two separate images can be uploaded as File:TestImage.jpg and File:TestImage.JPG. This has the potential to cause even more problems that the above situations. There is no reason why filetype extensions should be case sensitive.
Note: this is split off from Comment 71 of task T6421.
T6421: Image file extension should not be part of the name
T42479: File extensions should be automatically decided by MIME type at upload
T213484: Normalize file extensions (capital vs small letters; jpg vs jpeg) for new uploads on Commons
T34660: File extensions for the same file type should not allow variations of a file name (File:X.jpg, File:X.jpeg, File:X.JPG should all refer to the same file)
T31284: Upload form should change file extensions to the canonical form automatically (lowercase, jpeg→jpg etc.)
T144593: File extension changes automatically while moving ogg audio file on Commons, caused by a gadget