Let's assume that you have three images, named im1.png, im2.png and im3.png, which are the same size. You want to start the slide by displaying im1, and then "overlay" im2 and im3 as you click the mouse or the right arrow button. One way to do this is to create a slide for im1, copy this twice, and inserting im2 and im3 in the two copies. However, this creates several nearly-identical slides, and you would probably also have to manually resize and position each image in the exact same location. If you have several images, this approach will be very time-consuming.
A better way is to add all the images to the same slide, and to display each one in turn using animations. You then want to add an animation for each image after the first one. For example, you import im1 to your slide, then import im2 and add "appear" as an animation, and repeat the same for im3. Pretty simple! The main annoyance here is that the images should be exactly the same size and in exactly the same position, to get the proper "animation" effect.
Rather than adjusting size and position for each image as you add it, you can first add all the images with animations, and then change size and position for all images simultaneously:
- Add the images in the order in which they should be displayed. For every image after the first, add an "appear" animation
- Select all the images by drawing a selection rectangle, right-click and choose "size and position" (or something like that, I currently have a Norwegian version of Powerpoint :)
- Adjust the position. Since all the images are selected, they are now shifted to the same position (for example zero offset from upper left corner) and are perfectly overlapping. You can reposition the images later by selecting all and dragging them to a new position.
- Adjust the size so that the images fit nicely on the page
With this approach you can make a 10-image animation in less than a minute.