How to avoid embedding an image in Apple Mail

Dear list members, I'm using an iMac 27" Late 2012 (OSX 10.8.3). Since recently, probably after an update, Mail started to automatically embed images in my messages. Not long ago it didn't do that and even gave me the option of choosing image size (small, medium, large, original); this option is gone too. How can I go back to the old configuration and avoid this automatic embedding? I just want to attach images, not embed them. Could you please help me?