you must create it in Adobe Photoshop or some other similar program.. how to do it, i don't know, you can search on the internet websites that can explain you how to work with this program.. or ask it to someone who know how to make them..
then you can use Imageshack to create the link to put in your profile
**we all start as 'noobs'.. and we will end 'noobs' again..**
or wait, iam preparing page with tutorials just for the crims, and you can post image on Uploader , here images dont be deleted and you get link with tags, so copy and paste
or u can use TinyPic - Free Image Hosting, Photo Sharing & Video Hosting it-s more easier !
Good Luck !