I was going to reply to Sean's comments on filenaming conventions in this Lightroom forum thread:

Nothing wrong with using yymmdd-camera sequence, lots of people do.

I generally just use Custom Name_YYMMDD_3 dig Seq (or 4 for larger shoots)

It's not a pedantic point either - I'll assume his “generally” using a filenaming convention was a slip of the tongue - but I'm more interested in the two conventions he contrasts.

Either method satisfies the basic principle of no two pictures sharing the same file name, and I happen to follow something similar to the first - YYMMDD_A081234.nef where the “1234” came from the camera-generated “DCS_1234.nef”. The additional letter is “A” or “B” and allows for the chance of two camera bodies shooting a DCS_1234.nef on the same day. Yet I often wish I'd gone Sean's way from the start as it results in a shorter unique file ID and gives you the possibility to check you've not accidentally deleted any items - in accountancy (eek) we used to call this a “sequential continuity” control. However, Lightroom users who renumber the files in this way have a problem if their hard drive crashes. Here's a true story….

A couple of weeks back, a friend/client had a hard drive crash. He shoots 6-900 pictures a day, 4-5 days a week, and had just lost 2-3 weeks' worth of client pictures. But his Lightroom catalogue was safely backed up, and he restored the originals Lightroom had backed up as part of its import process. Sounds wonderful? Well, not quite.

The problem was that after editing down each shoot to around 300 pictures, he renames them YYMMDD-0001.cr2 through YYMMDD-0300.cr2. His newly-restored Lightroom catalogue was looking for those file names, but his restored originals still had the original camera-generated names like KLKJ1244.cr2.

Now in my case, my filenaming convention is repeatable and I could have renamed the restored originals - DCS_1234.nef would again become YYMMDD_A081234.nef. LR would then have had no trouble remarrying its thumbnails to the renamed backup files, and the whole job would have taken a few minutes (I'd have done it in Bridge or in a new, temporary Lightroom catalogue).

But in his case, he had deleted hundreds of rejects before he had renamed the keepers. To reconnect Lightroom's thumbnails to the originals, he would have needed to examine each thumbnail in turn, allow for tiny variations between frames (he uses two Canon 1D Mk III tripod mounted-bodies), and then rename the original file so it matched the new 001-300 name in Lightroom. For one or two images that might be acceptable - but for thousands?

This is clearly a downfall of Lightroom's backup upon import feature - as a minimum it needs a corresponding feature that switches its thumbnails back to the original file names. As it stands, with this unrepeatable filenaming convention you need to back up the images again immediately after renaming them. In my friend's case, he happened to know someone who knew the original filename was stored in Lightroom's catalogue and who could also write the SQL to restore it and overwrite the current filenames….