Any time you use another person’s photo, you should ask the photographer’s permission.
You should also publish a photo credit line, sometimes accompanied by awebsite URL, with the photo.
It’s the photographer’s equivalent of thebyline for the authorof a written work.

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Photographers and copyright holders often require specific wording or offer suggested phrasing to accompany photographs or illustrations they supply.
It may also appear as part of the caption or elsewhere on the page.
If several photos from the same photographer are used, one photo credit is sufficient.
In this case, it may be necessary to reverse the credit line out of the image for legibility.
If it isn’t readable, it doesn’t count.
Specifically, look for these terms: