With next version of AMASS (soon) you'll have a gallery image selector inside the post editor, so you can use that to see if the image you are going to upload is not in you gallery yet.
When you click "Pick from gallery" you get the paginated gallery browser under the post text. It is the logical place to have it as it can not be a floating tool like others, it would cover too much space. In that way it can have customized pagination, folders (later) and other info there.
The gallery images are, when clicked, inserted as GALLERYIMAGE tags with a 5-character identification code (fixed for each gallery image so they can be be reused via copy/paste too).
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