By Sue Manning

By Sue Manning | Associated Press

Tuna the hound peeks out from beneath his blanket. He bares his row of buck teeth for the camera.

Courtney Dasher rescued the dog in 2010. The mixed-breed pooch has bug eyes, a big nose and infamous overbite. Four years later, the dog from California is dubbed a "Chiweenie" in hashtags. He is the most popular dog on Instagram.

Pet owners are unleashing their pooches on the photo-sharing service. They set up accounts to show Manny the French bulldog sporting spectacles. Or Tuna poking his schnoz out of a suitcase.

Funny pet photos get plenty of play on Facebook and Twitter. Those include "muttbombs." That's where people Photoshop dogs into snapshots of themselves or celebrities. Shelters and others use them to promote adoptions or rescue campaigns.

Animal lovers eat up the snapshots of dogs doing the darndest things. And that gives Manny and Tuna insta-fame on Instagram.

Dasher, who says Tuna resembles Mr. Burns from "The Simpsons," started @tunameltsmyheart in 2011.

"You would never hear me call Tuna ugly," Instagram spokeswoman Liz Shepherd said. "He has unconventional beauty. Some people say Tuna is the best part of their day."

Handsome is the word Dasher uses. "He's so unique, and I love that and everything about him," she said.

Manny, once rejected by a breeder, is now the world's most followed French bulldog on Instagram. Amber Chavez of Chicago says her dog looks like a cross between a bunny and a piggy.

Manny's owners use their dog's account to aid animal charities.

Loni Edwards of New York City follows Manny, who has been posed to look like he's sipping a soda. She said silly or cute canine antics put her in a good mood. There's plenty of that from Manny. He spins on his back legs to a rap song in one short video.

Chavez and Dasher say motivation for their posts comes from their dogs or the fans.

"Every time we turn around, he's doing something cute or funny," Chavez said. Plus, Manny "gets excited when he sees a hoodie or outfit coming his way."