Can I use a web page that was saved at a given time as legal evidence on court? How do I prove it's authenticity? I prove it's authenticity?

I produced a derivative artwork for commercial purpose in which I used a photo from Flickr, an image hosting website. The photo used is under Creative Commons Attribution License. It essentially allows anyone to utilize it in anyway, even commercially, as long as it credits back to the original owner. Recently, it has come to my attention that changing the licenses overtime is, although rare, possible on Flickr. At the event that the owner changes the license to non-commercial use, how do I keep an authentic evidence of the web page stating that the license of the photo at the time of use allows for commercial use? I would need to do it to prove I have not violated the initial agreements of the original license. Please help me on this. Thank you!