In the options, under the graphics tab, TankPit allows customization of many graphics. There are currently 7 theme presets you can choose from, and also a custom option. If you choose custom then you can mix and match many different sprite sheets (graphics sets) that the game hosts, or you can even use special sprite sheets (graphics sets) that you have on your computer that you (or another player) has created.
Using Custom Graphics Sets Edit
First you must download a sprite sheet (graphics set) image onto your computer in a place you'll remember. Then go to http://tankpit.com/play Click on the options icon found below the bottom left corner of the game. Click on the "Graphics" tab. Click the drop-down menu and select "Custom". To the right of the graphics set you want to change, click the "Choose File" button. Locate the sprite sheet you want to use in your computer and click "Open". Click save and play with your custom graphics!
Here is a tutorial video showing how to do it:
Although this tutorial focuses on the "tiles" and "tanks" graphics, the process for changing the others is the same.
List of Player Created Sprite Sheets Edit
Here are some sprite sheets that players have created but were not added into the preset options in the game:
Transparent/Ghost Tanks by sFear: Edit
This sprite sheet (on the right) allows you to see through your tank.
Here it is in action:
Sprites (Graphics) TutorialEdit
If you are interested in creating new sprites for the game, there is a very in-depth tutorial about it HERE.