The picture/logo will need to be in.jpg or .gif file format and uploaded somewhere to the web (ie.as a attachment to a FW post initially or copied from another site)
From there the URL address of the image can be added to your profile by right clicking over the image,properties,black out theURL address and then right click and copy to clipboard.
Edit your profile and then right click and paste in the address where indicated.
The picture size in the profile will be resized to a max of about 60 x 60 pixels.
Try it with my forum logo but add [img] and [/img] at each of the code for the forum use only,these image tags are added automatically in the edit profile box.