If the bank scans all checks into an imaging system, does the bank need to keep the original checks? If so, is there a specific way the checks need to be kept?

Check with your State laws concerning this. Some states have a retention requirement; other's don't. Also, if your bank creates substitute checks, are you ensuring that your copies are clear? If not, you may want to keep them long enough so that you could produce the original in case of a claim.
BC