That won't help much. • Compressing to a file size limit is actually difficult/expensive. Tools usually target some good-enough quality level, and then the fil

That won't help much. • Compressing to a file size limit is actually difficult/expensive. Tools usually target some good-enough quality level, and then the file size depends on remaining entropy in the image. The limit would need to be conservatively high. • Exploits aren't necessarily larger than an average image. Adversaries in this case are quite skilled, and may be able to codegolf it if necessary.