Open up the picture you want to add the selective gray with dashed lines effect in Photofiltre.
Using the Selection tool on the Rectangle setting or whatever setting you like, make a selection in the picture you want to make gray.
After that, click the Grayscale button,
Now click the button on your keyboard that says Print Screen. It will usually be near the top right hand corner of your keyboard.
Press Shift+Ctrl-V on your keyboard. The picture of the entire computer screen should appear.
Using the Selection tool, cut out your picture and press Shift+Ctrl+V again and you’re done!