Utilizing a copyrighted photo as a reference for your painting can be done legally, as long as you adhere to certain guidelines. The key is to avoid directly copying the photo and instead use it as a source of inspiration and reference. This means you should aim to create a unique interpretation of the image, rather than a direct replica.
When using a copyrighted photo as a reference, it's important to make significant changes to the composition, colors, and overall style of the painting. This helps ensure that your work is considered a transformative work, which is protected under the fair use doctrine. Additionally, it's advisable to use the photo solely as a reference and not reproduce it in detail or use it as the primary subject of your painting. By focusing on your own creative process and artistic expression, you can create a work that is distinct from the original photo and avoid any potential copyright infringement issues.