Batch trim transparent from images hindered by small artifacts

I have downloaded a lot of trees and people for use in image editing. (from places like vyonyx.com)

I am now converting all of these into a cad program (long story but just context for you!)

But I have a problem, I need to batch trim all the images to the bounding box of the actual image but the trim is currently being stopped because there are small patches of non-transparent pixels around as the images weren't originally cut out "properly".

Also, I cannot use a batch canvas size crop because they are all different sizes.

I need to trim the canvases of about 300 images to match a live trace of each of them.

suggestions:

either a way remove small patches of unwanted pixels

or

open the .ai illustrator file (contains a live trace, which I want the psd to match up to), trim the canvas, insert the associated .png file (same file name but different extension) at the same size. delete the .ai live trace silhouette layer, then save as a compressed .png and close.

I have been using actions but never scripted so very much a beginner for scripting here - if scripting is even needed.

Thanks for your help,

Luke.