I use Sharex on Windows and I don't think there's any better tool, so I searched for "run sharex on linux" and there is indeed a guide - https://github.com/ShareX/ShareX/issues/6531 - maybe you can get it to work?I believe it can do all of the things you want. Certainly area capture, remembered area capture, fullscreen capture, all bound to different hotkeys. Mine saves with the name = the timestamp but you can probably config it to be an incrementing index. It's incredibly full-featured.I also have hotkeys for "capture current pixel's hex code" and "measure bounded box in pixels." When you take a capture you can also annotate it including showing labeled steps. After capture you can do one or more of: save locally (to one or more places), upload (to one or more hosts), copy to clipboard, etc. That includes pastebin if you have text saved to your clipboard so I use this for that also.

Screenshot Test: Applications are not often screenshot tested. However, if the business requirement is there, screenshot tests can be used to diff two screenshots from the same application state in order to verify whether something (styling, layout, …) has changed. It’s similar to a snapshot test, whereas the snapshot test only diffs the DOM and the screenshot test diffs screenshots.