MicrostockGroup

http://microstock.geneimages.com/dir (not really "big 4", but "bigger 5")

The calculation is done in assumption that absolutely drunk inspector makes absolutely random acceptance decision.

For the top 5 stock sites, we calculate how many images that have aggregate earnings of more than $5 were rejected, and how many images of the same amount of worst images (no-sellers for longest time) were accepted

Results are compared with random decision - 1/2 error rate

Results:

Stock               DIR
123rf             96%
iStockPhoto        61%
Dreamstime       41%
ShutterStock      38%
Fotolia               32%

I'd like to see the accepted images that didn't sell in 3 months separated from the rejected images that made > $10 (a much worse inspection issue in my opinion).

The former would make any new site inspectors look drunk merely from the low # of sales.

Drunk Inspector Ratio 2

Second variation accounts only for rejections of good images, and does this proportionally to aggregate earnings of rejected image on other sites

Stock                DIR2
iStockPhoto       54%
Fotolia              53%
ShutterStock     40%
123rf                33%
Dreamstime      22%