It sounds like you are placing each image in its own layer in the timeline. While this is a good idea, you need to add a blank keyframe in the layer where you want to stop showing an image.
timeline.jpg 72.3 K
Each frame is a series of many vector graphics calls. Each shape is defined using lines & curves and placed in a frame using PlaceObject2 tag (see flash 10 specification). After all shapes are defined and placed, a ShowFrame tag is added to show the frame and objects within it.
This step is repeated for each frame (or slide).
I'm not sure what a "keyframe" translates to in the flash specification.
There is no "ClearFrame" or "ClearStage" tag available in the specification.
The only way I can see to accomplish this is to use "RemoveObject" tag to remove each object that was placed before creating the next frame.
While this might work is can be many thousands of objects...and quite burdensome.
You're clearly in the wrong forum. You obviously want to be asking this question in the Open SWF forum.