I can second Paint.Net. It seems like I have used that for 20 years or so. I call it an "Engineering" oriented image editor, versus Photoshop, which I call an "Artistic" oriented image editor. In my opinion, very excellent.
I also use tools that I find online to draw banner images with fancy fonts, or button images with rounded corners and shaded backgrounds.
Unfortunately, I can never remember the name of the good ones I have found. I always end up Googling for terms like "banner images" or "button maker". You'd think I would bookmark the pages so I can find them later

.
Barry.