Does anyone have any data regarding the  'acceptance' percentage of scanned images for customer usage?
i.e. out of x number of images, how many does the customer have to 'rekey' or 'rescan'?

We're trying to determine what is acceptable from an industry perspective.

Are you running CAR/LAR?
What is the makeup of your deposit?  All business checks?  All personal?  What is the percentage of each in an average deposit?
How good are your clients at keeping the scanner clean and properly serviced?

I have found the scanners to be very similar regarding item acceptance.  Digital Check built OCR verification and dynamic image thresholding into the firmware for their latest scanners.  Canon has some nice imaging options, but not much in the way of OCR verification of the MICR line from what I have seen.  I have not seen any image options for the RDM or Panani scanners, but both of those scanners are difficult to test since they don't provide demo software.

My experience with rekeying has been anywhere from .5% to 10% for MICR with Digital Check and Canon scanners.  Typically this number has been between 4 - 6% of documents have a MICR error, either rejected or misread.  The rejected documents are the ones operators will fix, but the misread documents are worse because that can result in the funds being withdrawn from the wrong account.  Misread items are not included in the percentages above.

These number sounds very high and if you talk to a scanner manufacturer they normally disagree with these numbers.  I would two, but I wrote an analysis program to identify documents with bad MICR characters and the results were normally at around 5%.  A couple things to consider are when I run a scanner the reject rates are much lower (typically around 2-3%).  A lot of times scanner operators are in a big hurry and they don't jog the checks well which leaves the checks misaligned.  This causes piggybacks, skewed images, and checks going through the scanner above the MICR reader.  All of these feed errors will cause MICR rejects.  This can also cause image acceptance failures.

When I first got into the industry about four years ago I heard the industry standard reject rate was .5% -- or a MICR acceptance rate of 99.5%.  This number was based on high speed transports such as the NCR 7780 or iTran, not desktop scanners, but it took me a while to realize that.  I also think that number was based on bad MICR characters / total MICR characters.  The numbers I provided above show bad checks / total checks so I don't think the scanner industry is presenting bad information, I just think it isn't very useful to an end user.

Rescanning is a little different.  The questions posed by Jaugustin regarding scanner maintenance, servicing, and check types (business checks can be very busy and the thresholding on a bitonal image can be difficult to get right) play a big role in image quality.  Another important factor is who are you using as an image exchange?  The FED is pretty relaxed with image quality right now while some of the banks are very strict with IQA.  I have no idea what the average acceptance would be for rescanning an item, but whatever it is, it should probably be higher.