In looking at the user manual for a Nikon D7000, I see that the camera can create multiple exposure images (where more than one image is exposed into the same frame) in-camera. I don't recall ever hearing that was possible with my previous DSLRs (which have all been Canon).
Do any Canon DSLRs offer the ability to do multiple exposures?
Short answer: no. Longer answer: You can fake it, to a degree, with long exposures.
In a nutshell, what you want to do start your exposure, expose the first part, then cover the lens with a dark cloth, reposition, and remove it to expose again.
It’s not as precise, it’s more work, it works better at night, and it might not be worth it. That said, you can get some neat effects with the technique:
(via dreamsjung)
I cannot speak personally for all models of Canon EOS cameras, but I do know that it's specifically not possible with the following Canon models:
Based on this pattern it'd be pretty easy to infer that the rest of the EOS line (and possibly other Canon lines as well) does not have this functionality. That is to say that it's 'not possible' in-camera without 'faking it' as outlined in @ieure's answer. Obviously with the use of post-processing it's fully possible to make double (or triple, or more...) exposures. Also (probably obviously) it's completely possible with any of the bodies in the EOS film camera lineup... But I know that's not what you're asking about... Just trying to be complete. ;-)
Yes, there are currently 30 cameras supporting multiple-exposures and 3 of them are from Canon.
Most models optionally adjust the gain to prevent multiple correctly exposed images to be combined into an over-exposed one. Fuji has a nice implementation where you can undo the last exposure and re-take it as often as you need to get it right.
Everything I've read says you can't. Here's a few articles I found from researching.
http://forums.steves-digicams.com/canon-eos-dslr/136216-multiple-exposures.html
http://photo.net/canon-eos-digital-camera-forum/004YCQ
http://answers.yahoo.com/question/index?qid=20080820092042AA3hfY2
This last article is interesting, if you really want to do a multiple exposure image.
From Canon October 2011 release
"The EOS-1D X is the first EOS Digital SLR to feature Multiple Exposure capability. The camera can combine up to nine individual images into a single composite image…"
Canon cameras that can shoot multi exposures:
Complete list: Canon models that are capable of shooting multiple exposures
Fake it in Photoshop.
To get this shot I tripod mounted and took lots of photos during the parade. I then picked the ones I wanted ghosted, and brought them into photoshop, carefully pixel aligned them, and then played with the transparency slider on each layer.
In regard to the comment about it being impossible for the 40D to take a double exposure...that is not true in my experience.
I took a very cool double exposure (coincidentally by mistake) of a painting I had done and of an old wooden floor and the picture came out awesome. In fact, I began to do several other cool shots likewise. So it is very much possible to take double exposures with the 40D and I bet with the Xsi as well.
Come to think of it, I have done it with the Xsi using lights as my subjects.
In a nutshell...it can be done totally in camera and without any need of software.
