I presume that each batch of photos will have a specific theme or a use case in mind. If I were looking for sharp photos for my web design consulting website, and I think Apple products are the standard for the industry, I might use these images. Conversely, if I were doing a basketball design, I might incorporate urban images (asphalt, chain link fence, generic graffiti) to invoke a particular mindset or attitude.
I would recommend displaying the license in which these high resolution photos can be used, because "free" isn't a license.