The Patient Photos node in the sidebar displays photos associated with a patient record as a Patient Photo. In Many mode, Patient Photos shows all patients with Patient Photos, whereas only the selected account's Patient Photos will display in One mode.
For information on adding a photo for a patient, see General Navigation - Camera Button.
If you want to delete a Patient Photo, simply select the patient in question in the sidebar under the Patient Photos node, and then click the red minus. This will prompt you to delete the photo in question.