I'm using a photograph of a famous personality for a poster I'm making. I'll be manipulating the photo, maybe using image trace to create a vectorized version of the image for the poster. This I believe would be considered a derivative. I found the same image in multiple places, how do I find the original source of such a photograph to credit it's creator for my work and not face copyright infringement? When I see the images in Google search it simply says this image may be subject to copyright. (Also, is there a specific way to credit the creator? Under what circumstances do I have to buy the image to use it?)
There is no name or watermark on the image. One of the highest resolutions of the image links to a wallpaper site. This is the image I want to use:
https://www.hdwallpapers.in/roger_federer_4k_5k-wallpapers.html
I'm really new to all of this and have just started learning graphic design. I'm really confused about copyright issues and I definitely do not want to get sued for anything.