Oh... I think I get what you mean, and it seems like you misinterpret the use of it.
sweatdrop
The #id_about img doesn't actually help you add images into the panel, but more like changing the property (if it's the right word) of the contents (which in this case specifically target the images in the panel only instead of everything including words).
sweatdrop
Say in the About Me section you have these:
TEXT TEXT TEXT
[img]Image Url here[/img][img]Image Url here[/img][img]Image Url here[/img][img]Image Url here[/img]
If you want to change the opacity of the About panel, you'd use this code:
#id_about {opacity: .5; }
But if you'd only want to change the opacity of the Images inside the About panel, you'd use:
#id_about img {opacity: .5; }
TL;DR: The #id_about img has nothing to do with adding images inside the panel.
sweatdrop (Correct me if I'm wrong, Yoshi. )
If you want to change the BACKGROUND of the header (the color parts where it says the names of the panels to an image instead of plain color):
#id_SELECTOR h2 {background: url(' IMAGE URL HERE WITHOUT IMG TAGS ' ); }