All the graphics the game uses are stored in the Graphics folder in your game directory. You can easily change them. This page is meant as a guide on how to do so, which graphics are stored where and also as a collection of edited sprites. If you did any sprite editing please share them in this gallery!
How to change the graphicsEdit
First find out which Image files contain the grapics you want to change. In a lot of cases, that's easy by browsing through the the folders in the Graphics directory, but might also be a bit tricky.
Now rename the file, then copy and edit the sprite, copy another sprite from the same folder or get a different sprite from someone else. The new file should have the exact same height and width as the original. Rename it, so it has the name of the image you want to replace and move it to the originals folder.
The Players avatar sprite is in the Characters folder. The normal walking overworld sprite is named trchar000.png/trchar001.png (male/female). The running, surfing, fishing, etc sprites are named boy_bike.png, boy_dive_offset, boy_fish_offset, boy_fishsurf_offset, boy_run, boy_surf_offset and girl_bike.png, girl_dive_offset, girl_fish_offset, girl_fishsurf_offset, girl_run and girl_surf_offset.
Other player sprites are trback000.png/trback001.png and trainer000.png/trainer001.png. The icon of the player indicating current position on the map is located in the Pictures folder an named mapPlayer000.png/mapPlayer001.png
This image will show you the basic to change your trainer and where to find them. Notice the black trainer's name and the default red trainer's name. If you're a female trainer, it would be trchar001.png that you have to rename.
The sprites used to display your pokémon in the party screen are located in the Icons folder. Corresponding to their national pokédex number the pokémons sprite can be found at iconXYZ.png where XYZ is their pokédex number.
From #651 onwards the icons aren't animated, that means pokémon in your team from the X/Y edition will be static and not moving.
Most of the menu frames are located in the Pictures folder.