Twitter user @_Caspar_ has a website that generates a variety of images using your own Halo 4 Spartan, decked out in your armor and colors, and avatar.
The Halo 4 Gamercards include stats with an image of your Spartan in your choice of default pose or the one you are currently using in Halo 4, and a variety of background colors.
The Halo 4 Avatars generator has similar options, but includes your choice of a variety of background images or solid colors.
Want to create your own sig but need an image of your posed Spartan? The Halo 4 Armor generator is the one for you.
Using the Halo 4 Emblems generator, you can generate your own Halo 4 emblem simply by entering your gamertag, or select from the Halo 4 options and view possible combinations to come up with something new.