Yeah, this is stupid. You can't sentence people for drawing and using a paper and pen, whatever the content of their drawing, ...
Sure "you" can. This was in the UK. They don't have First Amendment protections, so the law is what's passed and enforced.
Last I heard, some jurisdictions in the US have some similar anti-pornography laws, banning drawn images. In the US the anti-pornography laws are justified against the clear prohibition on such laws in the First Amendment by claiming the purveyors of pornography are part of a conspiracy with the pornographer who abused an underage child by photographing her.
Obviously this justification is bogus when the image is drawn. So while the prohibition is on the books, I understand the authorities are reluctant to actually enforce it against anyone who has enough money to appeal it. So they tend to use such laws only when they can't find (or plant) any actual child pictures on a target(s) they've raided, but still really want to jail them and seize their assets, or as a "pour on the counts" measure when knocking the law down wouldn't do much for the accused.
(I think the underage are underripe and have no personal interest in such fare. So I don't follow the issue closely, except when someone threatens to post such stuff on a system I administer. Maybe somebody else, with more reliable and/or up-to-date knowledge, can comment?)