The image of Heard, which was shot for Interview magazine, featured the actor from the waist up wearing a blazer with her nipple exposed. It had initially been posted to the magazine's Instagram account with a black heart emoji covering up part of the 33-year-old's breast.
Heard took the social media site's community guidelines to task by editing Momoa into the original photo.
She wrote: "In honor of IG’s rigorous and equitable Community Guidelines against showing the Female nipple ..and since mine enjoyed the brief privilege that’s afforded to my male counterparts...
"I decided to pay homage by replacing it with a picture that DID meet IG’s strict nudity guidelines and such careful gender policies.
"See my stories to vote on which edit you prefer the most ..and thank you IG, here’s to 2019!"
Heard went on to apologise to Mom for using his images, writing in the comments: "Btw, love you AquaHubbs! Sorry to use your pecs to make a point!”
Instagram's community guidelines urge users to "post photos and videos that are appropriate for a diverse audience".
The guideline reads: "We know that there are times when people might want to share nude images that are artistic or creative in nature, but for a variety of reasons, we don’t allow nudity on Instagram.
"This includes photos, videos, and some digitally-created content that show sexual intercourse, genitals, and close-ups of fully-nude buttocks. It also includes some photos of female nipples, but photos of post-mastectomy scarring and women actively breastfeeding are allowed.
"Nudity in photos of paintings and sculptures is OK, too."