Hi. Are the included images free to use when using the Codea runtime? Or should I make sure to create my own graphics before attemping to get anything accepted through app store?
there are some built-in sprites. try the sprite() function, and click on the brackets to access them.
thats all i know until now 
Most of the graphics are from Lost Garden - here’s their licensing page:
http://www.lostgarden.com/2007/03/lost-garden-license.html
Check the spritepack of the sprite you’re using for credits.
It is generally a good idea to make your own resources if you are submitting something professionally.