It will depend on what OS you are using. I'm in Windows 10, so can explain the method I use.
- Ctrl+Shift+S puts the screen in a mode where you can mark a square on the screen with your mouse to copy into the clipboard.
- If it's a small pic, it will be small enough to put in here by just pressing Ctrl+V. As an example: View attachment 15855
- If it's too large, I put it in MsPaint and use the resize tool to shrink it: View attachment 15856 like this View attachment 15857 This is 75% which I captured via Step 1.
The only problem with shrinking a picture is it can become grainy.
Microsoft prefers you to use a different paint program, but what I want to do is very simple, so I prefer MsPaint. Finding it is the problem. Right click on the start menu, select run, type mspaint in the text box and click the OK button or press enter. I hope this helps.