this is a very big stretch in my NOT LEGAL ADVICE opinion. I think uploading an image that has been modified by Nightshade is miles in separation from what the CFAA is actually against, malware, if I upload an image that may or may not have been modified by Nightshade and it just so happens that my intellectual property causes your program that steals my intellectual property to function incorrectly, is that really my problem? I'm not encouraging you to download my image and I'm not misleading you into believing my image is something it's not, much like someone would if they were attempting to distribute malware.
I am NOT a lawyer, and nothing in this post should be taken as legal advice nor do I claim to be or provide legal council.