Wouldn't that many differences fall within a caricature?
It's directly traced over the top of the original image! Doesn't matter what's changed about it after that point, it's derived from the original through direct copying. It's a "derivative work", so it's legally tainted from that point on. Once that's happened, you've got to fight pretty hard to claw yourself free of the grips of copyright law in order to claim "fair use".
If following the letter of the law, artists have to be very careful with reference art. You should use unlicensed images for inspiration only and never directly copy any portion of them, which includes proportions, forms, outlines, silhouettes, etc...
Yes it's silly and yes it's unlikely you'll be caught (
especially if you're a good artist with dozens of references contributing to each part of an image), but by the letter of the law you may be infringing.
When I worked at a super-large corporate developer, artists weren't allowed to even visit google images. All reference art had to be approved by lawyers before you could think about being inspired by it