Just to update I haven’t forgotten this. I had a semi-working prototype that would allow layer selection for shadows, but I have no idea why but it caused full Blender crashes. Have to re-think it.
No need to hurry , just when you have the time and a good solution. I can get by at the moment. It would just be much more useful with layer flexibility. thanks for your efforts. 
Thanks for your patience. I only really get to work on it at weekends.
Please delete a link to the old version of script in your first post.
Probably the best way to present your work would be to post a link to the current version of the script in the first post.
This forum has a lot of to try and test, and not all of us have a time to read whole thread and search for up to date version.
Also keep us better orientated would be great use versioning of your script, old script in the first post is numbered as v1,0, same as the last version in post #10.
Thank you.
Q: How can I refresh BG image?
When Equirectangular BG image is used, addon use only first taken snap.
I tried erase, node and all tree, disable BG option in Tool shelf … nothing helped to get correct BG when camera view is changed.
Second thing, that is not related to BG - I got a strange error when I hit Render button, but since I get it once for now …
Re - version in post one, fixed.
Re the BG change. At the moment, once you enable you effectively make the BG static, and so changing it after the event will mess it up. For now, set up your scene completely before enabling the shadow catcher (i.e. camera animation etc.) and then it should work. I’ll look at a fix, but without frequent polling, which would take CPU time, I’m not sure how. I’m thinking maybe I can trap camera/BG changes, but it’s going to take some work.
As an aside, this is starting to become what was a simple one click plugin into something more complex, and the suggestions here are good, and things I’d like to implement. However, this is a “spare time” project, and so if any python coders want to collaborate, give me a shout (and include a snippet that shows me you can actually work). I’ll remain project leader, but I’m happy to work with people.
Bear in mind, the whole project could become redundant as Blender development continues.
Did you replace your camera after enabling the shadow catcher? It’s about the only thing I can think of that may explain that. Maybe it needs a “reset” button to undo the layers/compositing etc. to enable you to start again?
Thank you for more details.
Sadly, this is not what can happen in real life. Sorry.
I’m not a coder, but it is a hard to tell blender to render one pass more just with background (world) without any object from camera view?
Sorry if it is too naive.
I was looking for a way to place cg into photo space, that is nicely previewed in 3D window, but downside of this is - only flat surface can be used for equirectangular textures. For backplate doesn’t matter how complicated surface (that catch shadow) is. And shadow can’t be adjusted in post, but since realtime preview is able its not a big deal.
(Now I noticed all vimeo’s videos are gone on this site? Hmm)
Hard life of developers …
I’m not sure now. Now, I tried to replace a Camera view (position, rotation), also I tried to change camera layer, but it works.
Can’t repeat that issue.
Probably something with old script. I run old script from text editor (because of fixed issue enable addon in user pref) it worked, but I couldn’t get shadow render pass with old one, so I started to search in thread for new one, that I placed to text editor too (as before old one) bla bla bla … I post it more for curiosity of error message 
Leave it.
after installing the .py file I do not find the addon list. How should you call?
maybe “Shadow Catcher”?
win7_64bit + blender 277.11
How did you install the .py? Manually or from user preferences. I’m not so sure I can help with a manual install on Windows (Linux exclusively here) but you should be able to download the .py, then from user preferences, install from file, navigate to and select the .py file.
Once installed you should find it in Render/Shadow Catcher.