Today I confidently said to my father in law that I could make it easy for him to insert photos into gmail. Sadly Google let me down here.
Root cause bug is here:
Basically no one has updated the gmail compose/onepick integration to read from photos.google.com data. Instead it only supports G+ photos and albums, which are not being created any more.
So I thought, let's turn on Drive integration and use Drive OnePick. Nope. It sucks. You don't get an inline image in the message, nor can you use the photo options you normally get.
Inbox does have something that works, but I'm not going to train my 80 year old father-in-law to use another email client right after I got him moved over from NetZero(!)...