Using a photo from Pinterest as a reference for a drawing does not necessarily violate copyright laws, but it is important to be aware of the source of the photo and the copyright status of the image. If the photo is copyrighted, you may still be able to use it as a reference, but you cannot sell or distribute copies of the photo without permission from the copyright owner. If you want to use a copyrighted photo as a reference and then sell your artwork, it is best to seek permission from the copyright owner or use a photo that is not copyrighted.
There are several ways to find photos that are free to use and do not require attribution. Some websites, such as Unsplash, Pexels, Flickr's Public Domain Group, and Pixabay, offer a wide selection of photos that are free to use for any purpose. You can also use a Google advanced search to find images that are legally licensed for reuse. When using a reference photo, it is important to use it as a starting point and to add your own unique elements and interpretation to the artwork. This will help ensure that your artwork is original and not a direct copy of the reference photo. Additionally, if you plan to sell your artwork, it is always a good idea to keep a record of the source of the reference photo and any permission you may have obtained to use it.