The best workaround I found so far is to add a new tag to some images in my gallery app (Aves Libre), then filter for that tag and take a screenshot of it. It is neither possible to order the images nor to scale some of them. But it is definitely better than nothing ;)

Thanks for the hint. I haven't used Google Photos in a while and its features sound like what I want: https://support.google.com/photos/answer/12637115?hl=en&co=GENIE.Platform%3DAndroid

However, it is not an open source app.