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Does this mean that they can sell my images to anyone they like, even my competitors?

No. Firstly, where images contain identifiable people, or are of subjects which are themselves protected intellectual property then the person or intellectual property owner will also have the right to control how the images are used. Professional models will sign a release form which waives these rights so that the images can be used commercially without needing to consult them every time, but under normal circumstances a photographer will not ask their customers to sign a release, and will only expect that the images can be used in their own portfolio and other promotions. Images may also be protected by privacy laws if they show a place not open to the public and by data protection laws if they show sensitive personal information.

Secondly, the contract you have with the photographer will usually include an exclusivity clause, which guarantees that with the exception of the photographer (for promoting their own business) you have exclusive use of the images, even if they don't contain identifiable people, for period of time. During this period, if the photographer wishes to allow a third party to use the images, they must ask for your permission (and you are entitled to ask the photographer to pay you a fee for that permission).

If you are concerned that after the exclusivity clause expires (and the images do not contain either identifiable people or your own intellectual property and are therefore not protected this way) the photographer may allow one of your competitors to use the images, you should discuss this with the photographer as many will be happy to add a non-competition clause to ensure the images can never be used by your competitors.