What are the image files (PNG/JPG) in the TeamsMessagesData folder of a Purview eDiscovery export?

Hi, I exported Teams chats from Microsoft Purview eDiscovery (new experience) with the option "Organize conversations into HTML transcripts" enabled. In the export package I see the path: Items.X.00x.zip\Exchange\user@domain\TeamsMessagesData\

It contains HTML transcripts and separate PNG/JPG files. When I open the HTML transcripts, the images are displayed inline.

Questions:

1. What exactly are the separate PNG/JPG files? Are they hosted content (inline images pasted into chat messages) extracted as separate items?
2. Are they duplicates of the images embedded in the HTML transcripts, or can they contain images that are not shown in any transcript (e.g. from edited/deleted messages or messages outside the export date range)?
3. Which load file fields reliably link an image file to its transcript and message (FamilyId, ParentId, other)?

Is there official documentation describing the structure of the export for Teams content?

Thanks!