In this Macromedia Flash tutorial you will see how to make a simple image transission effect in just a few steps.

1.
Start by importing 3 images in to the stage
file -> import -> import file

2.
Select all images on the stage, right click and click distrubute to layers.
Now right click every image seperatly and convert them to movie clips.

3.
Place them centered, on top of each other.

4.
Now we have set up the images, and we can get to the effect part.

In the timeline right click at frame 20 and create a new keyframe for each layer.
Now for the two last layers containing images right click at frame 40 and create a new keyframe.

In the timeline for layer 1, right click between frame 1 and 20 and create a motion tween.
In the timeline for layer 2, right click between frame 20 and 40 and create a motion tween.

5.
Select frame 20 for layer 1, (you may need to lock the other layers while doing this, so you select the right layer)

Now select the image movie clip we imported before, and go to the properties panel and bring down its alpha to 0 as shown below.

6.
Do the same for the image in layer 2 at frame 40.

Now test your flash movie and see how easy it is.