How to attach spotlight found document to mail message with os x yosemite?
As the other answers suggest, you can simply drag and drop into your mail message.  However, I found that this is not always the behavior that I want.  Sometimes I want to see the file in the context of its own folder, or get additional files around it.

Holding down the Command ⌘ key, while double-clicking on the Spotlight result, will open the containing folder of your image (or any file) in the Finder.  I use this function all the time.

As a bonus, just holding the Command ⌘ key will show you the path of the file underneath its Preview, as illustrated in the following screenshot.