Photo editing - no printing done

We often edit photos provided to us, or taken by us.

You might want something changed in a photo, a particular area left coloured and the rest turned into sepia or black and white, you might want two photos blended together, you might want part of an image added to another, or have text on your photo, or you might want the main subject of your photo in a circle or oval, but still surrounded by the square "frame," plain white "frame," or a different colour?