This is a series of posts which will list some useful apps for development and general usage of Windows. These are just some examples of what can be useful. Of course, use any app you already know or have.
image editor:
Paint.Net
Paint.NET is image and photo editing software. It features an intuitive and innovative user interface with support for layers, unlimited undo, special effects, and a wide variety of useful and powerful tools.
Krita
Krita is a professional FREE and open source painting program. It is made by artists that want to see affordable art tools for everyone.
IrfanView
It is designed to be simple for beginners and powerful for professionals.
IrfanView seeks to create unique, new and interesting features, unlike some other graphic viewers, whose whole "creativity" is based on feature cloning, stealing of ideas and whole dialogs from ACDSee and/or IrfanView! (for example: XnView has been stealing/cloning features and whole dialogs from IrfanView, for 10+ years).
IrfanView was the first Windows graphic viewer worldwide with Multiple (animated) GIF support. One of the first graphic viewers worldwide with Multipage TIF support. The first graphic viewer worldwide with Multiple ICO support.
XNViewMP
https://www.xnview.com/en/xnviewmp/
XnView MP is a versatile and powerful photo viewer, image management, image resizer. XnView is one of the most stable, easy-to-use, and comprehensive photo editors. All common picture and graphics formats are supported (JPEG, TIFF, PNG, GIF, WEBP, PSD, JPEG2000, OpenEXR, camera RAW, HEIC, PDF, DNG, CR2).
