You can add a picture everywhere your contacts are seen on your iPhone using a jailbreak tweak called Copic, available in the Cydia.

Add a Picture to Your Contact, Call, and Text Message List On iPhoneCopic allows you to put a picture to your contact that will appear on their name on your contact list, calls and text messages. This tweak works on the iPhone build-in Message app and other text message apps such as BiteSMS.

Copic, short for  Contact Picture, is available in the BigBoss repo for free.

(via iDownloadblog)