I'm not sure there is an issue if the images are properly licensed. That's why I made the distinction about photographers and marketing photography. For example, National Geographic Expeditions offers travel to Africa and uses some images from Piper McKay. The images were licensed through Getty and no attribution or credit is given. If NatGeo is marketing photography travel, they should disclose the photographer rather than imply the images are from the trip leader and are typical. On the other hand, if the travel is not geared to photography and photographers, and image making is secondary to the experience - I can understand the lack of photo credit.
The same idea hold for a website. I think photography related websites have a higher standard of disclosure than normal commercial use.