I’d probably recommend the following;
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Add a custom state to the repeating group called ‘imageList’ which has a type of image and is a list.
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Create a workflow that triggers on page load and sets the state of that repeating group’s imageList to Do a search for Images:items until #3's Image where your search constraints are the Type contains Arbitrary text and Image isn't empty. You also want to add the random sorting there.
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For each image in the repeating group cell, it should be Repeating Group's imageList:item #Current Cell's index

Should work fine but let me know.