The "Take a Picture with a Newspaper" method does not easily prove something is old; it is used mainly to prove something is new.
In the mag case we'd like to prove is was old ....or owned prior to 01JUL13.

I could take a picture of a mag with today's newspaper (01MAR13), and save the newspaper.
On 02JUL13 I could give that mag to "Joe" and have Joe take a picture with the saved newspaper from 01MAR13.

One could not tell the difference in date of ownership using the two pictures, if they looked at the two pictures on 03JUL13.

Since non-dated/non-serialized mags are indistinguishable, one could also not tell if it was the same mag in the early picture as in the later picture.

It is a good thing the "burden of proof" of violation rests on the prosecution, per 13-1224.