You'll also find people posing in gym wear, adverts for "diet" protein powders and posts about weight loss.
People do Veganuary for a wide range of ethical and health reasons. For some it's weight loss - especially if they're inspired by celebrities like Beyonce, whose pre-Coachella diet was described by nutritionists as potentially dangerous.
But is it a viable or healthy way to shed pounds in January, or in the long-run?
For Laura Banks, 23, losing weight was one of the main drives behind doing Veganuary, and she has been documenting her progress on Instagram.
"I do feel a lot more healthy," she says, three weeks in. "But I've had a similar weight loss to when I was an omnivore."
She says she feels adequately informed about maintaining a balanced diet because she studies nutrition at university, and stresses the importance of planning meals ahead.
One challenge she's found to weight loss, however, is the availability of vegan fast-food - especially since she doesn't have enough room in her student accommodation to store the fresh produce she'd like to buy.
Sam Calvert, spokeswoman for the Vegan Society, stresses that being vegan doesn't necessarily mean being slim, and that whether or not you lose weight by going plant-based will depend on what you eat.
"You can eat nothing but vegan chocolate and chips and be vegan, but you won't lose weight and it won't be good for you," she says.
She adds that veganism is a broader "belief" that goes beyond diet, and hopes that ethical considerations are the main reason people choose to stay vegan after January.
Harley Street nutritionist Rhiannon Lambert takes issue with celebrities promoting vegan diets.
She thinks Veganuary is founded on "good motives", but that doing it to lose weight is "not very sustainable" if shedding pounds is a long-term goal.
"Straight away if you have one month in your head, or one way of eating in your head, you're limiting yourself and making it harder for yourself to keep up those changes," she says.
She urges people considering going plant-based after January to make small changes such as meat-free Mondays.
This way your body can get used to having fewer animal products over time, rather than having to cope with a sudden change that can be a "shock" for the digestive system, she says.
She adds that people who do go plant-based need to ensure they get enough protein, iodine, calcium, B12, iron, vitamin D and omega 3.
Toni Vernelli, spokeswoman for Veganuary, says people who signed up through the campaign's official website receive daily emails about nutrition.
She stresses that going vegan "doesn't mean deprivation" but, like Laura, says it does require common sense and planning.