It would be MUCH easier and more secure if we could simply upload screenshots to POEditor rather than have to maintain a separate, external image store. CDN storage is very very cheap these days so should be affordable. I'd even prefer to pay more for that option if necessary.

You can easily add screenshots to a project if you follow the steps described here:
https://poeditor.com/kb/how-to-add-screenshots-to-a-poeditor-localization-project