Not a problem. Just hop on over to Aviary and use their online image editing software, Phoenix.
No, really. Basic Photoshop functions in a Flash app. And the quality is outstanding.
All you need to do is upload a photo and get right to work. Obviously it doesn't have all the bells and whistles of photoshop, but if you're in a pinch or just need to make some minor adjustments I highly recommend it.
There are also a couple of other neat online editing products they offer:
Talon - for screen capturing
Raven - for vector editing
Toucan - for color palette editing