Win a master rank Pokemon contest
OK so first you will need to win the Master Rank of the Pokemon Contest to one Pokemon then talk to the painter and it will be in the museum.
The art muesum is located at Lilycove City, at the top left.
In the Lilycove City, if 5 paintings of your Pokemon who won the contest are exhibited to the Art Gallery's second floor, the Curator will give you a Statue of a Legendary Pokemon... But about the Art Dealer outside, I still don't know what to do with him...
If you win it and overtake the other Pokemon by a lot, your Pokemon will be drawn and displayed in the Lilycove Art Museum. You will also receive a Luxray ball the second time you win the competition. (Just the competition, you don't have to get your Pokemon on display)
It is at the north end of the city at the right of the Art Hall.
He is the person standing near the mueseum on the outside. The curator is on the inside.
When you win first place in a Master Rank Pokemon contest, and do exceptionally well, there is a chance that the artist outside of the contest hall will show you a portrait of your winning Pokemon that he was inspired to make because of their (cute-/smart-/etc.)-ness, and will ask you if you want it displayed in the Art Museum. If you agree, then the portrait will be displayed.
Each game has a "featured" legendary that you can capture. This has been the case since the G/S/C games. Raquaza is the "Featured" Pokemon in Emerald. (Take not the Emeral Box art)
finish all the master rank contests for each category then go into the art museum and talk to the guy who took u into the upstairs room.
By winning the master rank of the contest of any type To get a picture of your Pokemon in the Lilycove Art Gallery, your Pokemon must win a ribbon in the Master Rank of its category. Note: This might not happen straight away. If so, keep at it; it wont take long. Most of the time when you don't win the portrait after the master contest is because you probably didn't have a lot of heart power of appeals. you have too have your heart meter towards the end if you want to have a better chance of getting your portrait.
Though fanart Pokemon drawings are open to debate, the official art for the Pokemon series is considered to be in the anime/manga style.
Anime