Close out of every program on your computer. Set your computer's desktop background as black. Press "PRTSC."
Open image editing software such as Paint on Windows or Paintbrush on a Mac. Right-click or Ctrl-click your mouse and select "Paste". An image of your desktop screen will appear. Save the image as "Before".
Download an image of the card you wish to use in the trick. Use a standard deck of cards so the image will match. For example, download an image of the 4 of hearts.
Open the image in the image editing software.
Set the image dimensions at 2 1/2-by-3 1/2 inches. These are the dimensions of a playing card. Save the image.
Close out of every program running on your computer. Set your playing card image as the desktop background. Choose "Centered" under the background options to keep the card the correct dimensions.
Press "PRTSC". Open the image editing software. Right-click or Ctrl-click your mouse and select "Paste". An image of your desktop screen with the card will appear. Save the image as "After".
Open a presentation program on your computer such as PowerPoint, Impress or Keynote.
Set the "Before" image in the first slide. Create a second slide and set the "After" image to take up the entire slide. Create a third slide and set the "Before" image once again. Save the presentation.
Click "Start Slide Show" before your spectators arrive. Give a wireless mouse to an assistant or place it under the computer desk where you can reach it with your foot.
Place the card you want to spectator to pick at the bottom of the deck. Keep your thumb pressed on the card and shuffle the cards by pulling stacks from the top of the deck and moving them down until you are left with only the bottom card. Slide the bottom card onto the top of the deck.
Press your thumb firmly on the top card of the deck. Cut the deck and as your remove the top stack keep the top card in place and push down to place the top card on the top of the bottom pile.
Present the pile to your spectator and ask that they draw the top card. Ask that the spectator keeps the card hidden from you.
Instruct the spectator to place the card back into the deck. Shuffle through the cards pretending to try and find the chosen card.
Act flustered as your shuffle. State that you have no idea which card is theirs and toss the cards gently at the center of computer screen.
Click the mouse with your foot or have your assistant click as the cards hit the computer screen to switch the image on the screen to that of their chosen card.
Gather the cards and press them against the screen and click the mouse again to switch back to the starting image and "transport" the card back to the deck.