Make a screen-shot and upload with a script

Solution 1:

simply run shell command:

screencapture -i filename

this will start screencapture in interactive mode (selecting region). See screencapture -h or man screencapture

If you realy need run the screencapture command from the applescript just use:

do shell script "screencapture -i filename"

you can test the applescript from shell:

osascript -e 'do shell script "screencapture -i /tmp/filename.png"'

Solution 2:

See my answer to the question linked to below which uses Automator to take screenshots and feed them automatically to the FTP script. Since you don't say that it absolutely has to be done by Applescript, I'm just offering it as a suggestion in case it covers your needs.

Seeking ambient screen recorder