Twenty years ago, when images were color slides and researchers went through drawers of images to fulfill a customer's request, there was great concern that duplicate images were stored at multiple agencies. Shopping around would net the best price. In fact, this almost never happened, even in cases where the same image was available in multiple agencies.
The same irrational fear exists today for different reasons.
Many portals are reluctant to represent images that might be offered on another portal at a lower price. However, given the huge volume of images of similar subject matter available on most, it is usually not that easy to find the same image elsewhere.
1 - First, each portal delivers search returns in a different order. So using the same keywords, an image may come up as number 10 on one portal but number 500 on the next.
2 - The date the image was uploaded plays a big role in where it will appear in the search return order.
3 - Even if an image is uploaded on two different portals on the same date, the number of images from other photographers uploaded after that date will alter the search return order.
4 - Sites that represent multiple distributors give each a different position in the search return order, changing the relative position for all suppliers between one portal and another.
5 - One of the biggest reasons for photographers wanting to put the same images on multiple sites is that when images with the same keywords are added, many older images will no longer be shown. If there are more than 4,000 returns to any given search, only the newest 4,000 will have a chance of being seen. Some might say that no art director is ever going to look through 4,000 images, but the sites never alter their order to bring some of the older images to the top. Thus, in order to give such images a chance of being seen photographers must place them on other sites.
6 - Most portals do not offer variations in the way search returns can be organized, so once an image works its way toward the bottom of the pack, it is effectively locked out of ever being seen.
Taking all these factors into consideration, it is highly unlikely that a buyer will be able to find the image on another site, regardless of price. Given the difficulty, most buyers won't go to the trouble to try, particularly if the initial price seems reasonable based on the buyer's planned use.
Given the above explanation some might view increased volume as the problem. They might argue for tighter editing. But tighter editing tends to keep new, saleable images off the site. If instead, we consider increased volume an advantage because it gives the customer more choice, the answer to making search easy as well as an opportunity to review a broader cross section of images may be to give the customer more options to adjust search return order.
At the moment most distributors reject this idea. But, being able to offer their customers a broader selection of imagery could help them generate more revenue. Distributors should want to help photographers maximize their income as a way of encouraging them to continue producing in the future.