I'm usually well behind the eight-ball with these things so apologies if I'm posting about something everyone else in the world already understands!
So, have you discovered Picnik yet? It's free online photo manipulation software.
It's a great way of sharpening up photos for your Etsy store - and they do say that clear photos lead to more sales. Here's the before (left) and after (right) shot of one of my pieces.
To be honest that's probably the most practical application. But they have some fabulously fun impractical applications too. Such as:
Turning an image into a pencil sketch (though I'm sure I had one for this piece at some point!)
Something called HSL - I have utterly no idea what this is, but I love her dark-blue eyeshadow colour now, so it's given me a new idea. Thanks Picnik.
Invert - again, not sure why you'd use this, but it's giving me ideas about new colour schemes, so it could come in handy. Actually, it's a great way of working out inverted light if you don't work from reference photos.
Duo tone. This one could be useful if you're doing one of those 'two colour only' jobs for a publication like Edtn Magazine
Add a frame - could be a nice way of displaying art work in a gallery style.
Curvy corners - personally I love these. They remind me of the photos you used to get in the 70s!
There are heaps more features - some only for those who subscribe - but most for free. And it's great for photo touch ups as they have a 'blemish fix', 'shine be gone', 'tooth whitening' and 'red eye' functions - I'll be using those ones regularly!