like you said its light leaks.
alot of people get free clips which they comp over the top of the image using either overlay or screen image option.
you wont get an organic look using the plugins so people shoot there own light leaks against black to them comp over picture.
if you want to try a pratical test look at this tut here:
You can get the same effect using shape layers with gradients. You need to animate the shape and experiment with opacity and blend modes and gradient fills. Can be done, but it takes a while to get an organic look. I have had several requests over the years for this kind of thing and I've never used stock footage or shot my own because I have wanted precise control over position, timing and look.
As DeepBlueSea said, you can do this with blend modes and stock footage and get an organic look, but he is completely wrong when he said you "wont get an organic look" if you create the effect entirely inside AE. Organic looks require a good understanding of animation and with practice and talent can be achieved entirely inside AE. They are just not automatic, but then good art is never automatic...
It may help to know where this effect came from. In the olden days, you could get fired for screwing up a shoot with this stupid, amateurish, careless handling of the resources entrusted to your solemn care.
Film was run through cameras after it was placed into light-tight canisters called magazines, or mags for short. There were two spools in the mag: a feed reel and a takeup spool. Four hundred- foot loads were on plastic center spools while 100-foot loads were usually on metal reels. Using a changing bag, the assistant camera operator or film loader would every so carefully configure the mags for shooting. I was taught to use the film can's adhesive tape to seal the mag's removable lids so it was clear to everyone on the set the mag was loaded with film. A mag that did not have tape around the lids was either empty or loaded by an idiot.
If you opened the lid and there was film in the mag, light would fog the film. When it was developed, you'd get chewed out, and you'd never do that again. One of the best sources for this effect is to collect heads and tails of mag loads. They usually get fogged in unexpectedly and unpredictably interesting ways.
How the light struck the magazine had a predictable effect on the film. If you opened the lid all the way, light came in all at once and exposed the top edge of the whole pancake of film. If your mag had the sprocket holes on the top edge, you'd get a fascinating artifact, little rectangular tunnels. If you just popped the edge of the lid open, you'd fog only an arc of the film's pancake and this would create a regularly oscillating set of fog artifacts, the streaks and blobs usually associated with this effect. The effect was slightly different if you fogged the exposed film in the takeup side or the unexposed film in the feed side. (Examination of fogged exposed film lead to an interesting lab practice known as post-flash. That was a way of getting one or two extra stops of exposure latitude. Risky but cool.) 100-foot metal reels offered some protection from stupidity and exhibited wild edge fog artifacts.
Lens whacking does not simulate film edge fogging, it's a completely different effect.
The problem with film edge fog effects, of course, is they are w-a-y overused, usually applied as a pointless affectation rather than an artifact of careless film handling or to deliberately simulate what happens when the film runs out or the camera runs out of motive power. There is another, far more subtle effect that happens when the movie camera runs out of power. The film slows down as it is exposed so it speeds up when it projected.
Message was edited by: bogiesan