To turn off the prompt, edit the following registry entry by removing "/prompt".
Scripts:HKLM\SOFTWARE\CLASSES\PortableWindowsScript\shell\open\command(Default) = <path>\ptclient.exe /playscript "%1" /prompt
Packages:HKLM\SOFTWARE\CLASSES\PortableWindowsChanges\shell\open\command(Default) = <path>\ptclient.exe /applyfile "%1" /prompt
Note that if the full program is installed, the shell extensions will point to pictaker.exe rather than ptclient.exe.
You may use a Package to make this change or hand-edit the registry.