Making A Postage Stamp
You can stop here if you want, but let’s really make the stamp pop out and give it a bit of a 3D look.
Next, go to Edit - Transform - Rotate 90 CW.

Next, go to Filter - Distort - Shear and create a middle point and drag it slightly to the right, as shown below:

Next, go to Edit - Transform - Rotate 90 CCW.

Next, go to Filter - Sharpen - Unsharp Mask. Enter an amount of 20, a radius of 50 and a threshold of 0.

After you’ve warped the stamp, double click on the “stamp base” layer to load its selection and then create a new layer beneath it called “shadow.” Hit Ctrl+D to feather the selection, enter a value of 4, click OK.
Next, fill this selection with the same black to white to black reflected gradient that you used on the stamp base, except this time, set the gradient opacity to 100%.

Finally, to finish off your stamp, set the layer mode of the “shadow” layer to multiply.

