For performance reasons our search engine can only access the first 1000 results of a given search. This is in fact just like Google and other major engines.
If you are trying to view more images, there is a few techniques to use. The best one is to try to narrow your search results. Maybe adding a another keyword. Or even specifing a date range - for example limiting to only recent images.
If you order the results in date submitted (decending or ascending) order, you may be offered a link on the last page to create a new search from that approximate point forward (it does this by adding/changing the date critieria of the search) - in this way you can get though by using a number of seperate searches.