Why pay or try to bypass Adobe's payment system when you can get a perfectly good photo processing app for free.

The Gimp is free and open source so you don't have to pay, though you can donate to help with its upkeep.

Whether it matches up to photoshop seems to divide viewers but unless you're a pro, I suspect you could be perfectly happy, I know I am.

It's available for Linux, Windows and Mac

Take a look The Gimp