How to batch rename images, in reverse numerical order?
You can use an Automator Workflow. 

Something like this:



Sort Finder Items step will sort image names descending (IMG_0003.jpg, IMG_002.jpg, IMG_001.jpg). 

Make Sequential step will rename them sequentially (IMG_0001.jpg, IMG_0002.jpg, ...).

Copy Finder Items step is optional, just to be sure not to mess with original files.