Arguably, the most famous decapitated robot (technically, android) head in science fiction is that of Data from Star Trek: The Next Generation : In the original question, you wrote, "
The girl did say it was quite famous and well-known...
" and in the in the comments you wrote, "...the picture (from memory) was very detailed, I recall there were wires and bits of metal coming out of its neck...
"
Data fits that bill on both counts.
As seen in the episode "Time's Arrow" :
scifi.stackexchange.com/users/40294/Praxis
Egyptian robot head from a famous StF work?
It has to be Stargate .
Check out the guard helmets:
scifi.stackexchange.com/users/24024/Broklynite
Heavy metal band, Iron Maiden's legendary, Eddie the Head .
Eddie's head is often disembodied and a lot of their cover art has Egyptian stuff on them.
In custom artwork such as a tattoo, I'd expect all sorts of wires and bits of metal coming out of his neck , as is the norm for depictions of him in fan art.
Eddie assumes a different guise relating to the themes of individual albums and their corresponding world tours, and has appeared as a cyborg, an Egyptian mummy and a lobotomised mental patient amongst others.
–
Wiki
scifi.stackexchange.com/users/23785/Mazura
Cybermen from Doctor
Who
A well-known robot that has often been seen with a severed head could be the Cybermen from Doctor Who .
Below are some examples: A Classic Doctor Who Cyberman-head from "Death in Heaven": A Classic Doctor Who Cyberman-head from "Dalek": Handles, the Cyber-head from "The Time of The Doctor": The Cyberman-head from "The Pandorica Opens":
scifi.stackexchange.com/users/54827/RedCaio
Battle Droids from Star Wars I-III
The Battle Droids, first seen in The Phantom Menace , look Egyptian with their long necks, thin heads, and markings.
The back of the head resembles a pharaoh's turban.
Battle droid heads are often severed during combat, especially when facing the Jedi.
Compare a Battle droid with Anubis: Severed Battle Droid head with wires sticking out: Battle Droid head close up
(the eyes especially look Egyptian to me):
scifi.stackexchange.com/users/54827/RedCaio
Well, there's IMHO nothing that looks Egyptian here, but Ash's head in Alien definitely has those wires you're mentioning, and that's for sure, a decapitated robot's head.
scifi.stackexchange.com/users/38169/Tloz
Sometime ago I met a girl who had the most stunning tattoo of a decapitated robot's head on her arm.  It may have been an Egyptian robot's head, but it was simply stunning.  I recall there were wires and bits of metal coming out of its neck.  The girl did say it was quite a famous and well-known sci-fi art picture but I am unable to find a copy of it anywhere.  Does this ring any bells with anyone at all?
Picture of a decapitated Egyptian robot's head with wires coming out of its neck
scifi.stackexchange.com
<robots><character-identification><art>
scifi.stackexchange.com/questions/100550
scifi.stackexchange.com/users/51380/Dr W
There are many possible answers to this question. The head in question could be taken from Stargate, Iron Maiden's Eddie the Head, the Cybermen from Dr Who or the Battle Droids from Star Wars. A number of sources are suggested including, Stargate, Iron Maiden, Doctor Who, Star Wars and Alien.
It's from the film Stargate. It is the singer Eddie the Head from Iron Maiden. It could be a cyberman from Doctor Who. It could be a battle droid from Star Wars. It looks like Ash's head from Alien.