Hello,  
You can use the following to get a user photo in base 64 format:
http://<host>/Adaxes/api/<WebUI>/directoryObjects/photo/data?key=<ObjectDN|ObjectGuid|ObjectSid>
where   
- host – specifies the name of the computer where Adaxes Web Interface is installed (e.g. adaxes.company.com);
 
- WebUI – specifies the name of the Web Interface (e.g. Admin);
 
- ObjectDN|ObjectGuid|ObjectSid – specifies the identifier of the object for which to retrieve the photo. You can use the object distinguished name (DN), GUID or SID as identifier.
 
Important: the approach will work only if you have Auto-Logon enabled for the Web Interface.