The cover (although not mentioned in the credits) was made by Dave Patchett, artist behind the fantastic Cathedral covers. Reportedly, Patchett's original cover only included Eddie and the monks,
I remember reading somewhere that Bruce said the CGI characters also belong to Patchett, but he only gave them to Maiden as a rough draft. The band apparently said they didn't want him to work on it any further because they liked the cover as it was... Patchett was unimpressed with the result and asked not to be credited.
Here's another few of Patchett's covers,
The Carnival Bizarre
The Garden of Unearthly Delights
...and to stay on topic, the album I'm listening to now
Forest of Equilibrium