If you've images or videos you want to encrypt for protection the best policy is to put them in a encrypted .dmg via Disk Utility. (Google it -- there are many guides online.)

However, the trick is to create an alias to the image(s) or video(s) somewhere on the desktop or in a folder (drag the file with Option+Shift held down).

When you double-click the alias, you'll immediately be prompted for the password to the .dmg archive, if it's not already opened. In other words, you haven't got to waste time manually opening the archive first.

The downside is that you'll need to manually close the archive after viewing by ejecting it in Finder. However, I'm sure that somebody somewhere has written a folder action or Automator action that periodically (i.e. every few minutes) attempts to eject any open encrypted .dmg mounts. If the file is open it'll fail. If it's not open it'll succeed.

set diskName to "YourDiskNameHere"
tell application "Finder"
	eject disk diskName
end tell

set disksList to {"Disk 1", "Disk 2", "Disk 3"}
tell application "Finder"
	repeat with i in disksList
		eject disk i
	end repeat
end tell

I like this hint.

Also, keirthomas wrote:
> I'm sure that somebody somewhere has written a folder action or Automator action that periodically
> (i.e. every few minutes) attempts to eject any open encrypted .dmg mounts. If the file is open it'll fail.
> If it's not open it'll succeed.

I would be VERY interested in this action! I have things saved on .dmg's that I must try to remember to close if I'm not coming back to my computer quickly. Something like this that would securely clean up after me would be nice to have. Anyone know of such an item?

TaoEffect's Espionage is a commercial product that uses disk images to provide seamlessly encrypted folders. It might be worth a look in this context.

I don't use this approach myself, but it looks promising (and free):

How to automatically eject a disk image,
http://www.practicallyefficient.com/home/2011/05/30/disk-image