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Photo Collage App for Android
(discuss.tchncs.de)
F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The client makes it easy to browse, install, and keep track of updates on your device.
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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 ;)