Electronic – the most amazing PCB artwork you’ve ever seen

Most artwork - with the exception of homemade boards - is done on the silkscreen layer, not in the copper layer, so should have no electrical effect. Artwork on the copper layer could increase parasitic capacitance in neighbouring traces.

Since it's rare for modern professionally produced boards to not have a separate silkscreen layer, I suspect the only people doing artwork in the copper layer are people producing their own boards - and they'll validate that it's not a problem simply by empirical testing.

It is a hoax, you can read more at Snopes and here.

But to add a bit of info, the story became popular in 1998, so the scale they would be working in was at best 250 nano-meters, so the picture would have been taken with an electron scope.

Here is the original picture:

The image is a clever digital manipulation of an image that appears on the cover of Darrell Duffie's book

...

It's a clever prank playing off the idea that a couple of Apple aficionados could surreptitiously sneak an anti-Bill Gates message onto the world's most popular CPU, where it could be seen only through a powerful microscope, but it's a hoax.

Here's another link with more information.

Semiconductor manufacturing improvements by year:

10 µm — 1971
3 µm — 1975
1.5 µm — 1982
1 µm — 1985
800 nm (.80 µm) — 1989
600 nm (.60 µm) — 1994
350 nm (.35 µm) — 1995
250 nm (.25 µm) — 1998
180 nm (.18 µm) — 1999
130 nm (.13 µm) — 2000
90 nm — 2002
65 nm — 2006
45 nm — 2008
32 nm — 2010
22 nm — 2012