Is there a standard minimum size for pictures of faces to be scannable/recognizable in a list? Scanning a contact list, for example.
- Screen resolution will play a role.
- Image resolution will play a role.
- The user's optometry prescription will play a big role.
- A whole mess of other factors could have any number of influences on recognition.
- Different influencers may result in a single user being able to recognize avatars under "situation A" but not "situation B".
If your list depends on the recognition of images, it's a bad list.
If any old number will do, pick 48px.
I made an employee contact list where we used 32x32 icons. It was important to be able to scan and recognize individuals on the list. One is able to recognize individuals. The key point here is that we used the employee ID photo so the face filled the entire image.
(As a side note a lot of people complained about the use of their id photos.)