I was shocked today to find out that using the function in the file manager to 'Replace' an image does in fact do nothing of the sort!
Rather than replacing the image in all of its applications within the system, it instead creates a duplicate using the same filename that DOES NOT replace the image in any of its application within the system.
This seems like a fundamental flaw in the either the functionality or if not, an error in the labelling of the action. Actually being able to replace an image would be incredibly useful. Granted there may be the need to include a 'Are you sure!' warning similar to when making changes to a template but I believe this would be avery useful option to have. Frankly I'm surprised no-one has highlighted this previously.