Where do I find the requirements for disclosing the fact that on a certain account we offer we will not provide images of checks in the monthly statement?

As far as I know, there's not a requirement. Under the UCC in most states, a statement that provides the check number, amount and date of payment is sufficient for check entries (see UCC, section 4-406(a), as enacted in your state).

However, customers may have certain expectations based on the types of statements they have received in the past. In the interests of avoiding misunderstandings and ill-will at a minimum, I'd suggest that you inform customers of the fact they won't get images (or that images cost more). Be prepared to tell them how to obtain images when they need them (using your online banking system or contacting Depositor Services, or ...).

I'm with John in that I know of no such requirement. Your deposit agreement may specify what responsibilities each party has pertaining to the account, including this. Our product descriptions told customers if an imaged statement wouldn't have check images.

Aside from that, Texas has a state law that (3, I believe) item copies per statement will be provided the customer, upon request, at no cost. Your state may have a similar requirement.