Is there a tool out there that can batch change 100s of images by just changing 1 pixel or adding something to the image to make it unique?
I betcha Photoshop can do it! It has a lot of scripts and actions.
Just record an action in Photoshop and use the File > Automate > Batch tool to do all the images. E.g. open an image and record: Change hue/saturation > set saturation to +2%. Save and export for web > save to desktop with whatever settings. Then Automate > batch > choose that action in the list, select folder as source > go.
Yup, that's probably the easiest way to do it.
If you don't have Photoshop, the free tool IrfanView is very powerful for batch image conversion. As with the Photoshop example above, you could just set it to Sharpen +1%, for example, then run it on as many images as you like.
Alternatively, if you're comfortable with a command line, this kind of thing is what ImageMagick was built for. It's not exactly user-friendly, but once you've written your batch file once, it's only a double-click away...
I use Automator in Mac OS X for those types of changes.
Listening to that...i'm preparing something soon.
XNConvert
Rename for mac