post processing - How do I combine multiple exposures for action shots?

I'd like to create one of those "stacked" action shot images where multiple exposures are combined to show the subject moving across a static background. Here's an example I found on Flickr (by Laurence Asuncion): http://www.flickr.com/photos/dfunkpinoy/2755832144/

Ideally, I'd like tips both for the photography part of this and for post-processing. For example, I'd imagine I want to shoot manual w/ the same exposure for all shots (as with a panorama), but I'm not sure if there are any other helpful tips for taking the shots. At one point, for example, I thought I'd have to tripod-mount the camera and keep the same framing for all shots, but I've now seen several examples where the composition moved from shot-to-shot.

I'm also interested in recommendations for post-processing -- software, technique, etc. I can envision a manual process where I stack layers and align them by hand in Photoshop Express, but I'd be surprised if there wasn't a better way — maybe using a pano tool like Hugin.

Answer

Everything that applies to shooting a panorama applies to shooting one of these. A tripod makes assembling more convenient but means you can't pan to follow the action. It's important to rotate the camera and not move your feet in order to make sure the shots line up. Locking the focus is going to be necessary. Same with shutter/aperture.

I've only done one of these, it could have been shot on a tripod but the location didn't allow it! I loaded the images in Photoshop, auto-aligned and then manually masked the overlap areas, this was quite easy as the frames are just the right distance apart to minimise overlap. A bit of overlap adds to the effect, too much can make it hard to see what going on.

Here are the original shots:

Photoshop's built in panorama tool has no trouble aligning the images:

A drop shadow has been added to show where the edges are. As you can see there was a little panning. I did not shoot the images but I did the post production (and modelling :) the actual photos were taken by a friend of mine. Here are the images blended together:

Here are the masks used:

I did a bit more blending, rotated the image, and filled in some missing sky/foreground and adjusted the contrast slightly, here is the final image:

The camera settings were 1/800s f/8.0 ISO200 22mm

I would be possible to automate the process of overlapping the subject by subtracting the common background areas and layering up the frames in chronological order.