The photo shows Geary breastfeeding the couple's infant daughter, Mia Love Thicke, while lying down in bed. Geary is topless in the photo and covers the breast not being used to nurse.
She captioned the photo, "MOM pic by baby daddy, Robin Thicke."
The photo, which has been liked more than 6,000 times, caused a storm in the comments. Some were all for the 23-year-old model's attempt to normalize breastfeeding, but others thought the photo was indecent.
Geary took to her Instagram story to seemingly reply to all the haters.
"It's just a boob," she wrote. "Calm down y'all."
Geary has often shared her her breastfeeding experience on social media.
The model previously shared the below snap of herself nursing her one-month-old daughter on April 1.
Geary keeps it casual in the snap, tossing on a pink-heart Snapchat filter as Mia nurses on her right breast.
The young mother is currently on vacation in Los Cabos, Mexico, and decided to play into that setting for her caption.
"Girls gone wild: spring break edition," she wrote.
She also posted the photo into her Instagram story with an equally playful caption.
"A little boob to kick off spring break," she wrote.
The photo has already received more than 3,000 likes on Instagram.
Geary seems to be all about motherhood on her Instagram profile. She regularly shares updates about Mia, including one about how Thicke's son from his marriage to Paula Patton, Julian Fuego Thicke, was bonding with the infant.
In the black-and-white photo, Julian is shown lovingly leaning his head towards Mia. Geary detailed what all the big brother has been doing with his newborn sister.
"MY HEART! I am so blessed!" Geary wrote. "Julian is such an angel to his little sister. He sings to her, reads her books and holds her until his arms get sore! I love my little family."1comments
The sibling shot has been liked more than 5,500 times on Instagram.
Geary and Thicke, who have often been criticized for the age gap between them, have dated for several years, but there are no signs that they will wed any time soon. They seem to be solely focused on raising Mia, at least for the time being.