If you right click (or ctrl click with a one button mouse) on the image you can select to view the image as icon, which makes it behave like a normal attachment. To make this the default behavior you?ll need to use the Terminal to set the preference. Terminal is in Applications>Utilities. Open Terminal and type:

defaults write com.apple.mail DisableInlineAttachmentViewing -bool yes

That will make every attachment you send act like an attachment instead of a pretty unusable decoration.

If you decide this isn?t what you?re looking for, to restore inline attachment viewing type:

defaults write com.apple.mail DisableInlineAttachmentViewing -bool false

Restart Mail and you?re back to normal.