Indecipherable

The doctor's handwriting was indecipherable.

The second and third quarters of the shield are indecipherable on the stone but clearer in two other representations of the arms, a painted wooden funeral hatchment for Mary Davie[…]

One of the last remaining members of the Navajo Code Talkers, who used their difficult-to-learn language to form an indecipherable code that helped the Allies win World War II, has died.

The explanation some are suggesting is that the object takes on the appearance of what is behind it, or that it takes on the appearanec ^([sic]) of what the observer thinks is behind it. In both cases, the object is still visible. It's a visible representation of what's behind it, but it is still invisible, just indecipherable from its surroundings.

If you knew who Jerry was you'd swear you'd been cloned. Your posting style is virtually indecipherable from his.

A British university compared lads' mags with comments from convicted rapists. It found that people could not distinguish the source of the comments. That is, Zoo uses language practically indecipherable from that of sex offenders.