set this_file to "/tmp/com.zuzara.desktop.png"
set ftp_host to "***"
set ftp_user to "***"
set ftp_password to "***"
set ftp_path to "/***"
set ftp_newfile to do shell script "date '+%Y%m%d%H%M.png'"
try
do shell script "screencapture " & quoted form of POSIX path of this_file
tell application "Image Events"
[...]
screencapture + ftp upload in AppleScript