If *attaching a caption to an image* presents an accessibility issue--then why not create a new type of text box, that just has different space parameters? The leading between the lines should be tighter, and the space between the text and the frame should be much smaller. That would be all you had to do to make a caption box that can be added in layout. That shouldn't cause problems for screen readers. The current option of a mile of white space between images and the *normal* text box caption substitute looks ridiculous.
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