Here are a few I had in my spam:
Girls battle for your heart: choose Aleksandra or Nilla (pic of young girl, maybe underage, maybe not)
Are You Older Than The Women You try to sleep with? (could be interpreted as a solicitation for child porn)
Enjoy Free Live Chat with Asian Women (pics look like young girls, possibly underage)
Meet Hottest Russian Beauties (this pic is definitely over 18 - yikes)
Men and the women who love them... from "The Hard Truth About ED" (pic definitely older)
30,000+ Russian Girls Determined to Find Boyfriends (pics definitely show youngish girls)
None of these were child pornography in the sense of showing explicit imagery, etc. But in the hands of an aggressive prosecutor who wanted to nail me for something, could be painted a certain way. And they did exist on my hard drive, even though I had never seen them.