To create the effect shown above, where the outline 'magically' draws itself, do the following steps:
Choose a photo, ideally one with a lot of contrast between the subject and the background.
Re-size, crop and sharpen the photo in Photoshop or another tool, to get it looking the way you want.
In Flash, import the photo to the stage.
Modify...Document to re-size the Flash movie to match the photo.
If desired, draw a white rectangle in a layer above the photo, convert it to a graphic symbol, the make the rectangle semi-transparent by modifying its 'alpha' setting, so that it's easier to see the outline as you draw it.
On a new layer above the photo (and also above the white rectangle if you have one) use the pen tool to draw the outline around the person, buildings, or whatever is in your photo that you want this effect for.
Modify the stroke thickness and color as desired.
Clone (copy and paste) this outline to a new layer, convert it to a graphic symbol in the library for safekeeping, and then delete the clone (but not the original) from the stage.
With the outline that is still on the stage, click on its keyframe in the timeline and hit F6 to clone the outline to a new keyframe.
With the eraser tool, erase a little of the outline, usually starting at the right end.
Click this new keyframe and hit F6 to clone this altered outline to a new keyframe.
With the eraser tool, erase a little more of the outline.
Repeat these steps of duplicating the keyframe and erasing more from it, until you have however many keyframes (typically 50 to 100), and the outline is completely erased.
Highlight all these keyframes in the timeline.
Right click on the selected frames and click 'Reverse Frames'. This will result in the line drawing itself instead of erasing itself.
If desired, fade the photo in as the line draws itself.