https://developers.google.com/people/api/rest/v1/people/updateContact
Here's the wiki on update contact using People API. The update works for fields like 'emailAddresses'. But 'coverPhotos' or 'photos' are not listed as valid value for 'updatePersonFields' and I get return code 400 if I try to update them.
Is changing photos of a contact supported by this API? Or is there any other API that does this job?
Currently you cannot update photos, there will be support for updating photos coming in the future. For now you'll need to use the old Contacts API to update photos.
The cover photo is only supported for profiles (it's the big background image in G+), so there isn't any way to set a cover photo on a contact.
Since Mid July 2019 it is FINALLY possible to update the contact photo with the people api: https://developers.google.com/people/api/rest/v1/people/updateContactPhoto
