Yes, OmniFocus will display the image as long as it isn't too large. Here's how you can set the value of "too large":
http://forums.omnigroup.com/showpost...05&postcount=7
If you embed the attachment rather than linking it, OmniFocus will keep a copy and you can delete the original. You should exercise restraint in the number and size of files you embed, however, especially if you sync between multiple copies of OmniFocus.
To embed an attachment, either hold down the option key while dragging the file into the notes field (you'll get a different cursor when doing so) or use Edit->Attach File... and choose the option to embed rather than linking. You might want to check Windows->Attachment List to make sure the file is embedded (if not, it will not appear in the Attachment List) before deleting the original. When OmniFocus grows creaky, you can also use the Attachment List to find out where all of the attachments are and remove them if no longer needed.