The first, second, and fourth charges in the indictment[1] is for violating 18 USC 1466A(a)(1)/(b)(1)/(d)(1)/(d)(4), which are the statutes against producing/distributing/possessing an "obscene" "drawing, cartoon, sculpture, or painting" "depict[ing] a minor engaging in sexually explicit conduct".
[1] https://www.justice.gov/opa/media/1352606/dl?inline