If you have a common identifier on both requests, for example a student number you can implement this by setting up 2 entities with an association between them. For example a student entity and a studentphoto entity. Make sure that the association starts in the student entity and ends with the studentphoto entity.
Make sure that the identifier you get from the call to get the student detals is stored on the student entity. Then when perfroming the call for the picture search for the student object by means of the identifier from the database and change the student object that is then found and set the association between the picture object and the student object.