Image Updates

I have approximately 100 jpeg images that I update every month (through Excel/PowerPoint) and can upload those to the Media Manager/Gallery successfully. However, the content (not file name) of these images change every month and I’m looking for a method so I don’t have to manually re-establish the link between these files and their use in a Gallery (or dynamic image). I would like to find a method (through media manager or collections) so I can just overwrite the same file name every month in either the media manager or collection. When I upload to media manager it creates a new data set and does not overwrite. It appears I can do this with a CSV file in Collections, but not images, even though it states that you can use any file type. There is a statement in “About Importing Data to Your Collection in the Content Manager” that says “You can import any field type into your database collection, except the following: Image field, unless they link to images that already exist in your media manager.” I don’t understand this restriction.