The following is to create animation so that under each animation, the image behind another image becomes visible.
1.)Open an image file containing pictures (in this example, Taj Mahal) and move it to photoshop document.
2.)Open another image file containing pictures( in this example,Nature) )and move it to photoshop document.
3.) create a new layer
4.) Draw a circle using Shift + Elliptical marquee tool or any shape you like.
5.)Press alt+ backspace to fill the circle with color.
6.) Right click the circle layer and select blending options and make necessary adjustments.
Use Bevel Option to give 3D effect. Use contour to get cool effects.
7.) Bring the circle layer between the two image layers( Taj Mahal image and the copy of Nature image).
8.)click on circle layer and alt+click between circle and image layer( or click add clipping mask).
9.) Deselect auto select layer option , click move tool, and move the circle.( see that the circle layer is selected to move the circle).
10.)you can also. create animation by moving the circle.