There are five ways to do this:
The first style is the simplest and easiest from with respects photography and editing. This is because the point of view of the NOW scene need not be exactly or even approximately the same as the THEN scene in order to convey the essence of change. Also there is no need for either image to be in the same chromatic scale – either or both can be black and white (greyscale) or colour. This style is usually seen in printed publication.
The second style is the most difficult for a number of reasons. It requires a degree of editing skill in order to create a plausible feathered transition from THEN to NOW. Only certain THEN images are suitable for this method in conveying change in that the subject matter must be able to show change by revealing a portion of the images. This style works best with greyscale THEN images and colour NOW images otherwise the change is not significantly obviously. And finally, the station of the THEN camera and the focal length of its lens must be as closely replicated by the NOW camera in order to get the static morphing effect of the change in other words the view point is important. This is the style for print or Internet presentation.
The third style is why this blog was created. It uses the mouse function to slide the one image over the other and back. It has the advantages in that the accuracy of station and focal length is not as stringent, the view point can be a little off and the morphing effect is simply created by a sliding one image over the other. This is accomplished by using the jQuery TwentyTwenty Plugin. This style is for Internet presentations. The base images for Style 2 can be used as the images for Style 3.
The fourth style is similar to Style 3. It use the mouse-over function to slide the one image over the other and back. The slider in this style moves of it by placing the mouse (or touching) on and off the photo cause the slider to move back and forth and has a fader affect as well. This style is for Internet presentations.
The fifth style is achieved by using any of the free online slideshow software available.