Image editors or similar photo manipulation tools can way in at a hefty price, in particular the Adobe tools, whilst its hard to replicate the features of these tools most users only need more basic functionality.
These free alternatives should provide what most users need for their day to day tasks.
https://pixlr.com/ – A robust browser photo editor, for all your editing needs. With Pixlr Editor you have full control over your images including layers and effects, its online but there are also mobile apps available for IoS and Android devices (Web based)
Paint.net – An image and photo editing software for PCs that run Windows. I use this for simple tasks, its ease to use and has more power than the built in Windows Paint program. ( Windows)
Inkscape – Another big hitter in the open source world, this is the open source equivalent of Adobe Illustrator, that is its a vector graphics editor without the hefty price tag ( Windows, Mac, Linux)
https://www.gimp.org/ – GIMP is a cross-platform image editor available for GNU/Linux, OS X, Windows and more operating systems. Very powerful for a free product and particularly popular on Linux based OS’s. (Linux, Mac, Windows)
Pinta – a free, open source program for drawing and image editing .( Windows, Mac, Linux)
Canva – An online designer which makes it easy to create graphics for ebooks, social media sites and banners, a few of teh resources have to be paid for such as stock photos but there are plenty of free ones and you can supply your own (Web based)
Seashore – Seashore is an open source image editor for Mac OS X’s Cocoa framework. It features gradients, textures and anti-aliasing for both text and brush strokes. It supports multiple layers and alpha channel editing. It is based around the GIMP’s technology and uses the same native file format. (Mac)
Photoscape – a fun and easy photo editing software that enables you to fix and enhance photos (Windows, Mac)
Photopos – a free photo editor with many powerful features, one drawback is that you can only export up to a certain resolution unless you pay for the premium version, may not be an issue depending on your needs