Several bells & whistles for google photos.
Photos taken with Google Maps 360 photo tool
Also try #AutoAwesomeMovie
Your videos, unedited by google
Photos stored in google drive
Pictures you have posted to Google+ (I believe this is pre-Google-Photos only)
Photos uploaded from your computer
Media that was uploaded via google photos backup sync
Not sure about this one yet...doesn't seem to be fully functional
from Nov 5 2015 to Dec 2 2015
Google stylized photo
Google stitched Panoramic
Google auto-created collage
Google created GIF
Similar to "Motion" but not the same...I'm not sure what differentiates the two
I think the rule for figuring out what hashtag to use is to go to a picture taken with that hashtag & click the "i" for info, then copy the camera type. If it is hyphenated, don't change anything (#SAMSUNG-SM-G870A). If it has spaces, just delete the spaces ("Canon EOS DIGITAL REBEL XT" would be #CanonEOSDIGITALREBELXT).
ie: "Bill and Bob"
Find photos with 2+ named people together
Search contents of photo for anything (not just text)
ie: "Bill with dog"
Combine searching for named people and things