Images are distorted. How can I revert them all back ?

Hi Damien,

My images were all optimized but many of them are distorted; especially the gifs (please see attached). I have changed my settings. But, first, I need to revert all images back to the originals so I can re-compress them (with the right settings, this time). So, how can I bulk-revert them all back ?

Also, question for future reference: If I wanted to bulk-revert only a certain type of images (e.g. all the gifs), how would I be able to do that ?

Thank you,

Helen