There is no one-size-fits-all answer to this question, as the legality of using copyrighted photos on a blog will vary depending on the specific situation. However, general rules of copyright law apply in most cases, meaning that you generally need permission from the copyright holder to use their photos on your blog.
If you’re not sure whether a photo is copyrighted, it’s best to contact the copyright holder directly to ask. In most cases, they will be happy to provide you with permission to use their photo on your blog.
However, if the copyright holder is unreachable or unwilling to cooperate, you may need to take other measures to protect your blog’s copyright infringement liability.
One common tactic is to include a link back to the original source material on your blog post. This will allow readers who want to learn more about the photo’s copyright status or licensing agreement access to the original source material.
Additionally, you can use Creative Commons licenses when sharing photos on your blog in order to allow for wider sharing and remixing of the images without requiring permission from the copyright holder.