Select a large picture to vector. It must be at least 600 by 600 pixels, so that you can see a lot of detail.
Save a copy of your picture as a different name. This way, if you want to start over, you'll still have the original image.
Copy the background layer of the picture, and then turn off the visibility.
Click on the "Posterize" option under the Image and Adjustments menus.
Use the pen tool to outline the biggest parts of the photograph. Begin a new layer of outline for each part of the image, using the Layer option. For instance, if it's a picture of a flower, begin a new layer for the stem, the leaves and each petal. Use a color similar to the color in the detail for each outline. Using the Layer option allows you to work on each detail of the picture individually, without touching the other details.
Continue outlining the details of the photograph, starting with the largest ones and ending with the smallest.
Adjust the colors of each detail to add highlighting.
Use the gradient tool to add highlighting to the background. Select several colors that are in your picture to use in the background.
Use Photoshop brushes to add details on top of the background. Be sure to use colors that coordinate with your picture.
Save the image as a .VPF file.