In the Blood and Wine expansion, you cannot access Mount Gorgon in Toussaint by normal means. However, there is a small grassy field on the summit of the mountain that can be accessed using mods. If you teleport Geralt there, you can find a blank canvas with a red blotch on it sitting in-between two columns. Using Witcher Sense to view the canvas will reveal a completed painting: a group picture of the game's developers at CDProjekt Red.