While it's certainly possible to do this in matlab using dir, a for loop, and some simple path manipulation, there are plenty of tools freely available dedicated to renaming files which will be simpler to use and more importantly, don't require debugging (hence no risk of losing files because your script all rename them to the same file).
Personally, I would use IrfanView because I've got it installed on my machine (I'm in no way affiliated with the product) and it's trivial to do what you want with it. Use it to open any of your image. Press B, select batch rename, select all the files, select output directory. Write $d$N in the rename field. Press 'Start Batch', and you're done.
