A note about photos -
The most important pictures for authenticating bags depend on the style and age of the bag, but in general are:
the entire creed stamp or patch and the serial number - always use the Macro setting on your camera.
the allover pics of the bag - front, back, sides and inside including the lining to show any stamped or woven patterns
the hardware, especially anything like clips, zippers, buckles, O- or D-rings with the
Coach name stamped on them, the strap ends and buckles, and the inside pocket zipper and zipper pull
we expect most bags to have zippers
stamped YKK even if the bags are fake, but a few fake YKK zippers can be spotted in a good clear close-up. Usually a pic of the zipper and the metal or leather zipper pull is better than an extreme close-up of the YKK or other zipper manufacturer stamp. And yes, there ARE other zipper manufacturers
all paperwork like price tags (both sides), receipts, other paper, metal or leather tags, "authenticity" or Care cards, and the dustbag if there was one
the top and underside of the turnlock, especially on older bags
any unusually wrinkled or otherwise "off" areas on the bag especially on older leather bags
the metal "feet" on a bag if it has them
any areas on the bag with uneven, loose or doubled stitching or anyplace where the stitching doesn't look right. Also, if a bag has stitching in some areas that's elaborate and unusual compared to the average Coach, please take pics of those areas
and yes, the hangtag and the ball chain, although a hangtag by itself should never be used as proof of authenticity. A hangtag can be changed or replaced in 5 seconds and often hangtags on older bags have been lost or damaged.
Certain style bags may need pics of other specific areas. To really be sure that a bag is genuine can take about a dozen photos.
Other posters may be able to add more suggestions, and I'll post a full list at the "Answers..." thread.