The exact wording is unambiguous. However, you are quite correct
"You can earn achievement bonuses based on the number of likes your photos are given."
"You can earn achievement bonuses based on the number of likes your livery is given."
(Bold emphasis is mine)
I just did these tests.
I liked one of my own photos, and my "likes on photos" count went +1
I liked one of somebody else's photos, and again, my count went +1
I liked one of someone else's livery and my "Likes on Liveries" score went +1
Easy money, I'm thinking. I was trying to be really compellingly artistic to get rewards from these achievements. Turns out I can earn achievements by liking any old crap