The NASA pic is the blue marble. You can find it in many places on the web since its a public domain image. I made a post about one of the higher res versions here tho:

http://www.cartographersguild.com/showthread.php?t=3834

If you have attached the pic on the site then it must be < 5000 pix but the one linked to is about 180,000 pix wide. I.e. its silly. You can opt to get lower tho. So if you need the marble in high res then head on over there.