First of all, I recommend you contact an attorney for guidance on what is required for privacy of images.
With that said, a signed release is a safeguard against potential issues. If you do not have a signed release and you post photos of individuals without their knowledge or consent, at the least you open yourself up to possible complaints and requests for photos to be removed from your page. A strong set of procedures at implementation will help avoid issues in the long run.
Many financial institutions do not post images of individuals at all or place strong restrictions on what they do post. A few things to consider:
1) Some financial institutions post photos of employees. Other’s feel that may be a security concern.
2) Depending on the circumstances, posting photos of bank events may indicate that the person in the photo is your customer.
3) The Children’s Online Privacy Protection Act (COPPA) places restriction on what you can collect, including photos, from children under 13 without their parents consent. Facebook has rules and procedures in place to comply with COPPA as well that include allowing parents to request their child’s (under 13) photo be removed.