OS X: creating or extracting preview(.jpg,.png) of .eps file

Like codelogic mentioned, sips is a good tool for this. However, it doesn't support EPS natively, so you need to convert to PDF first.

If you're on Tiger or Leopard, something like the following should work:

mkdir pdf jpg

cd pdf
echo ../eps/*.eps | xargs -n1 pstopdf
cd ..


sips -s format jpeg *.pdf --out jpg/

Assuming your EPS files are in the current directory, this will first convert them all to pdf, storing them in the pdf/ directory, then convert each PDF to a JPEG file in the jpg/ directory.

ImageMagick should be exactly what you're looking for. Once you have it installed, just use the convert utility:

convert file.eps -resize 25% preview.jpg  # create jpg thumbnail at 25% size

On OS X, you can use sips to perform image processing tasks, like thumbnailing. It should support EPS. If it doesn't, as Adam recommended there is ImageMagick's convert.