If you still have access to a scanner, you can have some fun playing with this idea. Take a piece of paper or a white card and paint on itI mean with real paint (or great big markers). Scan it in (after it's dry of course) and use that as a shape in a layer mask. (Hint: Scan it at a higher resolution than you think you'll need so you have some room to play with resizing.)
Here's the result of my scan.
Take a look at your scan and see what you've got. If necessary, as it was in this case, use Curves to brighten up the area around your shape. Click on the Set White Point eyedropper icon at the bottom right of the Curves dialog, and then click with the eyedropper on a color in your image that's not as white as it should be (the background around your shape should be nice and white).
Press Command-A (PC: Control-A) to Select All, and then Command-C (PC: Control-C) to Copy.
Switch to your photo, and while holding down the Option key (PC: Alt key), double-click on the Background layer to rename it. Click on the Add Layer Mask icon at the bottom of the Layers palette to add a layer mask to the photo layer. Then, Command-click (PC: Control-click) on the Create a New Layer icon to add a new layer below your photo. Press D to set your Foreground and Background to their default colors, and press Command-Delete (PC: Control-Backspace) to fill it with white.
Press-and-hold the Option key (PC: Alt key) and click on the layer mask thumbnail to view the contents of the mask. Press Command-V (PC: Control-V) to Paste the scanned shape that you copied in Step Two. Don't deselect yet.
Press the Tilde key (~) to view the layer mask as a colored overlay, and then press Command-T (PC: Control-T) to bring up Free Transform. Use the handles to resize the graphic. (Hint: If you can't see the Free Transform handles, press Command-0 [PC: Control-0] to Fit on Screennow you can see and work with the handles.) Press Return (PC: Enter) once you're done, then press Command-D (PC: Control-D) to Deselect.
Option-click (PC: Alt-click) on the layer thumbnail to view the results and you'll see the opposite of what you want: the area inside the shape is masked, rather than the other way around. Click on the layer mask thumbnail to activate the mask, and then press Command-I (PC: Control-I) to Invert the mask and get the result you want. (You could've also inverted the image back in Step Two before you copied it so that when it was pasted, the mask would be white on black. Then this step would be unnecessary.)
Try applying a filter to the layer mask. Here I clicked on the layer mask thumbnail and used Filter>Artistic>Rough Pastels.
Add a layer style to the layer. In the second example, I clicked on the Add a Layer Style icon and added a drop shadow and an inner shadow.