While it’s not related to programming, editing images is an activity that I encounter when creating my front end.
Photoshop is great, but sometimes I find other software easier.
Lunapic’s Color Change is awesome if you have a color that you want to replace in an image. All you have to do it select the color you want to use in the image and then click on the color (in the image) you want replaced. Voila!
Pic Monkey makes it super easy to convert an image into another shape. My typical use case is changing an image into a circle shape (cropping the corners). To do this, you just click: Frames > Shape Cutouts > [circle icon].
If you’re looking for additional functionality, similar to Photoshop, I recommend Pixlr (use on the internet) or Fire Alpaca (download and use locally).