DXL is the best way to do it.

HCL Notes/Domino 8.5 Forum (includes Notes Traveler)

Subject:

For the problem images in your DXL export, do they result in a <gif> element in the output, or a <notesbitmap>? If the latter, I believe they are actually image references instead of actual images; the notesbitmap data is not a gif, but contains a binary header and URL in a Notes-specific format.

You coulddecode this information and fetch the image from the URL, and manipulate the DXL output to include a <gif> or <jpeg> element instead, or whatever's appropriate. But I generally suggest it's a bad idea to archive data that was only referenced in the original data. It makes your output bigger, wasting space on graphics that are usually either signatures or parts of useless commercial mail. If you wanted to delete useless data that bloats your archive without adding value, these are precisely the images I would choose.

Feedback response number AGUD8PGK35 created by ~Julia Prefootherlen on 12/12/2011