"can I use lithium batteries in a digital camera that specifies use of Ni-HM and Alkaline batteries without da

If your camera uses AA sized batteries, then yes, you can use AA sized Lithium batteries (e.g. Energizer e2 Lithium).
They're quite expensive, but last a long time.
High powered NiMH (e.g 2700mAh) are more cost effective though...because they can be used and recharged over and over again.
Never use Alkaline batteries in your camera. They are completely useless because they don't provide enough power for a digital camera.

yes you can they are the same voltage the just last longer

yes. usually lithium will last longer but make sure the voltage is same