I've always been a fan of the inserting image lab, so I naturally wondered if it would be possible to combine the two.
Today we're launching a feature that allows you to drag images from your computer into a message. You don't have to have the insert image lab enabled for it to work. Just drag the image in, resize it if you want, and send.
Currently, this feature only works in Google Chrome, but will be coming soon to other browsers.
Source : http://gmailblog.blogspot.com/2010/05/drag-images-into-messages.html