Along with the information window, a dialog can be put up to get the whereFrom text, with a little AppleScriptObjC (since a shell script has been posted in another answer) to add it. Extending the Automator folder action in my answer to your previous topic, the replacement Run AppleScript action would look something like:
use AppleScript version "2.4" -- ...
Keynote on your mac is maybe a good way to make a lesson. You can make slides of your lecture and record your voice lectures with it. You can then record the whole slide show as you go through it. It has a great LaTex equation maker with all the symbols you'll need.
I hope this is what you are looking for.
The following appears to work. I've done it twice -- once to show the shadow more explicitly, and then once to show the desired, finished output.
# adds the shadow
convert source.png \( +clone -background black -shadow 100x40+0+16 \) \
+swap -background none -layers merge +repage output.png
# adds the additional space like MacOSX
convert output.png -...
If you open /System/Applications/Utilities/Screenshot.app, you will be given the option to choose where your screenshot goes. You can select for the screenshot to automatically open in Preview.
Now anytime you use your keyboard shortcuts to take a screenshot, the default action would be to open the screenshot in Preview.