James I think 50 points can only be awarded for a bit of photographic evidence!
In the old days at the end of the I-Spy book when you had finally scored your 1000 points there was a verification process to be gone through:-
"Each book had pictures of items to spot and a box to record the time, date and place. Sometimes there would be a supplementary question to verify that the little Redskin {this is what the I-Spy tribe were known as} hadn't been "economical with the truth". Each spotted item also gained them a number of points: generally five or ten points for something common (a fire engine, say), but 20 or 30 points for valued rarities (perhaps a particular design of Gothic bootscraper found only within the lychgates of 15th Century Northamptonshire churches).
When the book had finally been completed, it had to be countersigned by a parent or teacher beneath the following sworn affidavit:
I certify I have examined the record in this book, and as far as I can judge, the entries are genuine.
The book was then mailed to Big Chief I-Spy, c/o the Wigwam-by-the-Water (later Wigwam-by-the-Green), London EC4. By return of post, the Brave would receive a coloured feather and an order-of-merit certificate franked with the chief's personal seal."
I only ever got my 1000 points for "I-Spy Birds"....
Regards Neil