If you use Firefox, there is a great little Addon called Picnik (v2.3), which allows you to right click on any image and edit it all online.
In Chrome, you can use the Picnik Extension for Chrome.
Both versions allow you to edit images without having to login or sign up for an account as well.
If you're used to using the internet for reference, but have been frustrated by having to move the image from the internet to Photoshop, this little addon will greatly reduce the time fiddling with images online. Need to flip an image horizontally? Adjust contrast? You can do a lot all within Picnic without having to leave your browser!