In the United States, copyright laws state that the photographer who took the original photo generally holds the copyright, unless they have explicitly given permission for its use. Therefore, creating a painting based on a photo without the photographer's permission would infringe on their copyright. While artists can certainly use a photo as a reference to learn about the characteristics of a subject, such as the shape of a tree or the texture of a rock, they must be careful not to copy the photo too closely. If an artist duplicates a photo in detail, replicating every aspect without adding unique elements, it can be considered copyright infringement.
To avoid copyright infringement, artists can get copyright permission from the owner of the photograph before using it as a reference for a painting. This may involve contacting the photographer directly or using a stock photo service that provides permission for commercial use. Additionally, artists can create their own reference photos or use free images from sources that allow commercial use. When using reference images, artists should analyze the photo and use it as a base, while adding their own unique elements to create an original work of art. It's important for artists to be aware of copyright laws and to always get permission when using someone else's work as a reference.