All My Photo File Extensions Were Changed?? Why!

Months ago I uploaded 1 main product photo for each of my listings. (My shop is not open yet, work in progress).  For example, I have things like:




Now that I'm going back into each listing to add alt image tags, I have junk like this:



Why is this happening? My files were correctly saved on my computer and uploaded in the proper manner and now there are all kinds of extra numbers and letters that I did not put there and I don't really want them there. Doesn't that hurt me in search results with all that clutter hanging on my file extensions? If anyone could help me correct this, it would be absolutely appreciated, more than you know! I have no clue how to correct this or why it happened. Thank you all for reading!