you can use IMG codes, but it works for pictures ON INTERNET. From your computer it will not work, so... Post your wanted picture anywhere on internet and provide it's URL in IMG code. Like this [img] your URL [/img]
One important thing... TGA mostly cannot be Imaged - Why I say so, cause if you screenshot a pic in wc3, it is TGA (Targa). You need to convert it to JPEG. I have Irfanview and it works good and can convert pics also.