Make sure you edit the script to match your version of Isadora. I am using the USB version, so you may need to adapt the application name in the script if you are using the standard version.

641ffe-watch-isadoracore-mediabinload.scpt.zip

Capture Camera to Disk to a Watched folder called (lets call it 'Moviefolder'): this places a filename.mov quicktime of 0.2 secs long, which is the minimum length that Isadora succeeds to capture.
Next step is that a folder action script watching the folder where the movie just arrived is triggered and calls a bash shell .sh file that extracts a couple of jpegs from the movie file and moves one of them into another folder called (lets call it 'PictureFolder'). That second folder uses the Applescript that autoloads any media arriving in that folder to load to Isadora's meda bin.
Ta da!  Now I have a jpg instead of a movie.

There are some more details involved. In order to process the .mov into a couple of jpgs, I installed Macports and then ffmpeg. Then I can use a bash file to tell ffmpeg to extract the jpgs from the .mov
I'll attach an example .sh file and the associated Applescript file.
Have really enjoyed learning how to do this. It's empowering. :)

A word of warning however, is that occasionally the watched folder simply does not run the Applescript, which seems to be an Apple bug. It works 97% of the ime, but every now and then fails to run, on Mavericks and on Yosemite, which is very annoying if you have a long-running installation.

5c2eb4-convert-bash-applescript-example-jg.zip

try
        tell application "IsadoraCore USB Key"
            import media into document 1 from these_items
        end tell

on error msg
        display dialog "Error importing file into Isadora: " & msg
    end try

end adding folder items to