(d)Affirmative Defense.—It shall be an affirmative defense to a charge of violating subsection (a)(5) that the defendant—
(1) possessed less than three images of child pornography; and
(2) promptly and in good faith, and without retaining or allowing any person, other than a law enforcement agency, to access any image or copy thereof—
(A) took reasonable steps to destroy each such image; or
(B) reported the matter to a law enforcement agency and afforded that agency access to each such image.
That may be the case in the US, but FWIW it is not necessarily true across jurisdictions. In the UK, for instance:
> A person who views an image on a device which is then automatically cached onto its memory would not be in possession of that image unless it can be proved that he / she knew of the cache [...but...] the person would also have "made" the image in question. Subject to there being evidence of the act which constituted the making and the necessary mental element, an offence contrary to section 1 of the PCA 1978 is preferable and in most cases would suffice. [...] The charge of 'making' [has been] widely interpreted to cover such activities as opening attachments to emails and downloading or simply viewing images on the internet.
Further note:
> So, for example, in a "pop-up" case, it would have be to be proved [for the act of making] that suspect knew that accessing a website would generate "pop-ups" and that those "pop-ups" would depict, or be likely to depict, indecent images of children
That is far shakier legal ground than I would like to be on, especially for readers of this thread who would presumably be aware of the cache and where it has been hinted that the images may contain at best questionable content.
(d)Affirmative Defense.—It shall be an affirmative defense to a charge of violating subsection (a)(5) that the defendant— (1) possessed less than three images of child pornography; and (2) promptly and in good faith, and without retaining or allowing any person, other than a law enforcement agency, to access any image or copy thereof— (A) took reasonable steps to destroy each such image; or (B) reported the matter to a law enforcement agency and afforded that agency access to each such image.
https://www.law.cornell.edu/uscode/text/18/2252A
Also, the main charge of possession is knowingly possessed