Painting

Paintings are objects from Super Mario 64 and its remake that work like portals. They are used to get to the many levels in the game.

Super Mario 64 / Super Mario 64 DS
Paintings in Super Mario 64 are used to travel from Princess Peach's Castle to the game's many levels, such as Bob-omb Battlefield. Certain paintings are located in special themed rooms (for example Jolly Roger Bay's painting is in what appears to be an aquarium). Most painting frames are yellow, but some of the paintings also have different colors, such as Wet-Dry World's being blue.

Paintings return as portals in the Super Mario 64 remake, serving the same purpose. One noticeable difference is that the Jolly Roger Bay painting is replaced by bubbles, which was the painting that was used in the Japanese version of the original game, instead of a galleon.

Super Mario Odyssey
Paintings return in Super Mario Odyssey. They serve the same purpose of acting as gateways to each of the game's playable kingdoms (excluding the Moon Kingdom, Dark Side and Darker Side), but they are not the primary means of traveling to each kingdom. Instead, they are scattered across each location, often in hidden areas. When used, they send Mario into enclosed areas in each kingdom, to collect Power Moons that are inaccessible through regular means. Before the game is beaten, only Luncheon Kingdom's painting (leading to the Mushroom Kingdom) is activated, all others are completely empty.

Paintings also appear in towers and other hidden areas outside Peach's Castle. They transport Mario to tougher versions of the battles against Knucklotec, Torkdrift, Mechawiggler, Mollusque-Lanceur, Cookatiel and the Ruined Dragon. When these paintings are used, the level select jingle from Super Mario 64 plays before the rematches begin.

There is also a painting in the Wedding Hall in the Moon Kingdom which allows for Bowser to be fought again. Another painting can be unlocked in the Wedding Hall by collecting all 880 Power Moons in the game (not counting extra ones obtainable by shopping) which leads to a harder version of the Bowser fight.

Luigi's Mansion
A single painting makes an appearance in Luigi's Mansion, the one Mario is trapped in, which serves as Luigi's primary goal. After Luigi defeats King Boo, Mario is sent through the Ghost Portrificationizer in reverse to return him to normal. Unlike the static images of the Portrait Ghosts, Mario's picture is of him banging on the panel trying to escape.

Luigi's Mansion: Dark Moon
Mario gets trapped in a painting again in the game's sequel Luigi's Mansion: Dark Moon. Mario's painting is alluded to throughout the game, but is fully revealed during the Secret Mine. After defeating King Boo, Luigi has to use the Dark-Light Device on Mario to get him out of the painting.

Trivia

 * In Wet-Dry World's painting, the Skeeter is shown to be a dark pine green, although they are actually an aquamarine color.