It's weird, no error message now, even though I didn't change the code. But it still doesn't display the image. I've checked transparency, position and the image doesn't blend into my wallpaper.

Even if the meter image don't need to be bound to a measure, you can make one to be useful for your skin.
My suggestion for your case is to have the following code in your skin (see below...), if cad is "off" it will show your image, and if cad is "on" it will hide your image, so your image will be not in the way of the display of cad.
And on a final note, if your cad image is in the Rainmeter skin folder that you made, you don't need to put the full path of the image, but only the name of the image will do !

Thank you for the help, the image is displayed now

But, (sorry if I'm being a pain) opening CAD.exe makes the image config non-draggable and doesn't hide it. It probably not important because CAD covers the image anyway.

Thanks again.

...No pain here !

Now the previous part of the code that I have posted was a modification for testing CAD in a Winamp + album cover skin that I made and use in my sidebar to replace CAD, and it had a transparent background image.
It almost the same thing apart the process is winamp.exe, to have the Winamp icon colourful when is "on", and colourless when is "off".
I don't know how your .ini file look like, so I have done a skin for the cad image and it work o.k (hide the image and you could drag it when the image is there), but if I remove the [MeterBackgroung] in it, the cad image will not be hidden, and could not be drag when cad is "on" like you said !
Here the skin so you can try it !

And here you can have a look of my Rainmeter Sidebar with Winamp + album cover skin...
http://www.kwikpiks.com/files/47/Rainmeter_Sidebar.jpg

Thanks heaps, works perfect now.