I keep a file like that too. But only for the 
ones I was *really* interested in which I would 
be interested to try for again. (Not EVERYTHING 
I've missed.) In the titles of the images, I keep 
track of: where I saw it sold, how much it sold 
for, the date it sold, and (if I know it) who 
bought it. So the image names resmeble something 
like this:

CCS-Animanga-$190-120102-Sempai.jpg
or
CCS-YJ-22200yen-$190-120102-Rinkya-Sempai.jpg

(The second would be for Japanese sites, to keep 
track of both yen and USD prices, as well as 
who's using what deputies, to better guess how 
much the deputy added on to the purchase.)

If the cel is resold, I will create a second 
image with the new information. For me, it's a 
way of keeping track of the sales history of the 
cel, which can be VERY useful to know if/when I 
get a chance to negotiate for it. ^_~

Many Sharp Smiles,
--Drac