I think this is a "feature" of the stock app.
if you go directly to the stock sms app and type in the number in the "To:" field, you should also see names and/or numbers pop up as you type. again a "feature".
I am on sprint, and i have not seen this image popup when i am in the stock app, just numbers and/or names as i start to type the name or number in the "To:" field...
If you want different options, you may want to look into other messaging apps or perhaps root your device.