While the internet is a great place to share and collaborate, it is not okay to borrow photos from someone else's website or social media site without permission. Any time you use someone else's photo, you should ask the photographer for permission. You should also publish a photo credit, sometimes accompanied by a website URL, with the photo.
How to Give Proper Photo Credits and Avoid Copyright Infringement
A photo credit line identifies the photographer, illustrator, or copyright holder for images in a publication or on a website. It is the equivalent of the photographer's byline for a written work.
Publications typically have a standard format for the wording or placement of bylines and photo credits specified in their style guide. Photographers and copyright holders often require specific wording or provide suggested wording to accompany photographs or illustrations they provide.
When using on the Internet it may be necessary or desirable to place a link to the photographer's site or another source.