We have done this a number of times. We have a form that the lender must sign that spells out exactly what we are allowed to do with the image. For example:
I, _________, own the items described below, and as a benefit to the study, display, exhibit, interpretation, research, preservation and documentation of Omaha history, give and transfer to the Omaha Public Library non-exclusive rights with commercial gain to the digital images for reproduction, publishing, or broadcast in print, digital, electronic, or other media of said items. Digital files shall be available for use under the same conditions and terms as the rest of the Omaha Public Library collection, including for exhibits, research, academic and commercial publication and personal use. For these purposes I provide the Omaha Public Library duplication and publication privileges. I will retain control of the physical collection except for a temporary loan to Omaha Public Library to allow for organization and scanning of the items using digital images best practices standards.
Etc. etc. etc. plus any other restrictions or permissions (we tweak as needed). If you have a legal advisor, I would have them help you create a form that covers your situation. The main thing is to have your agreement in writing so that both the lender and the library know what is allowed.