Our filtering was done by the Wikimedians organizing the competition. We used last year's judging tool, which allows as many images per page as you want, which makes it easy to filter literally thousands of images a day. Only one person needs to go over each image (because we trust our organizers). You should immediately filter out the pictures that have absolutely no chance of getting to one of the top places, which means you'll have immediately filtered out 3/4 or more of the images. After that it's a bit more meticulous, but I'm sure one person can do it.
Ideally you should have in the area of 200 images for the final jury (I think this is the statistic for many countries, not just Israel).