POEditor is a cross-platform localization management tool, which was originally designed to localize .po file, but now supports many other localization formats.
Out of the formats supported by our translation management platform, the ones that support Context are .po/.pot, .csv, .json, .xls/.xlsx, iOS .xliff, .ini.
Although you can use the Context field however you want, we don't recommend using it to add screenshots or to make comments on a string. This is because the Context attribute of a terms is what makes it unique in POEditor, and there's a good chance of ending up with duplicate terms.
If you have some observations that you wish to share with your translators (including screenshots), the best practice would be to add them in the Comment section. The first comment will be preserved during export/import and and will not create any duplicates.