Thank you for posting your question! Yes, you should transcribe captions and I think they will be a valuable research tool. As to the format, do your best to transcribe the caption as it appears on the page. Feel free to share an example here. As you know, you can use the tagging function to describe images, watermarks, stamps, or any other non-text features, use the tagging function.
I hope this helps, and thank you for your contributions!
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