I suggest that the system let a new user upload a image inline as the rest of us do, except that the image is not actually inserted into the post immediately. Instead, the post goes onto the edit review queue. Reviewers can view the image and approve or reject the image content, and of course can flag as spam, leave a comment, etc, just like they already can when reviewing suggested edits.
I'm not sure what should be displayed in the post in the mean time. Possibly a box saying a uploaded image is awaiting review. If it is spam, nobody has to see it, but can still read the rest of the post and won't downvote due to missing schematic or whatever. Another option is to show the URL. That gives people access to the image, but could also give spammers underserved hits. I guess that really isn't so bad if the link is pointing to a image on imgur so that it can't be a bad URL. At worst you see spam, but there would be nothing to click on, the spammer can't track the action, and it's only a image so can't exploit a security hole in your browser.
I'd probably go with the second approach because the usefulness of being able to see a real image outweighs the relatively rare case of viewing a spam image, which you'd then quickly flag anyway.