Usually, if an image is scanned and placed online, the clarity is reduced somewhat, so I would assume that, if you could obtain a copy of the original image from the NHC, it would be much clearer, or sharper, and may show the number.
As for checking which other vessels were in proximity to the MARMORA at that particular time, you would have to go to the deck logs for such information. However, is there an indication of the exact date that that image was taken? If not, you would not be able to find out the name of the other vessel. However, these vessels tended to operate in certain packs (like wolves!), so you may be able to locate data on the deck log information in the ORN volumes, at the very least, and perhaps get some clues there.