All you have to do is use the img tags. I know of no sites that simply allow you to copy and paste images in. If you do then by all means show me as I'd love to see how they manage it.
I have a feeling that you are referring to being able to upload images from your hard drive as an attachment. Whilst some sites do allow that, we don't. The simple answer is that we don't have the storage room to handle it, especially when you consider we piggy back our resources off BigFooty and BigSoccer.
Ideally you will save the image and then upload to something like photobucket before linking it to here. Though I'm guilty of it as much as the next person, hotlinking isn't really fair.
IMG tags work as follows -
TAG
www.picture.com/this.jpg TAG
So, to get this picture on here-
It would be [IMG]
http://news.bbc.co.uk/media/images/4...ietersen66.jpg [/IMG] (without the spaces)
Alternately, click the

button and then copy and paste the image location into the pop up box. That will automatically add the tags for you.
Remember that IMG tags will only work with a valid file type, i.e .jpg, .gif, .png and so on.