How many 747-200 are still in service?
Running the numbers from RedGrittyBrick's answer, there appear to be 36 active 747-200s out of 393 built (according to Wikipedia). Of the 36, 9&nbsp;are passenger planes, 22&nbsp;freight (including 6&nbsp;converted from passenger planes, marked *), 3&nbsp;combi (passenger and freight), and the two VC-25As ("Air Force One").

The active aircraft are as follows, with tail numbers included so you can look for photos.


Aerospace One: 1 freight (SX-ASO), 1 combi (SX-ASC)
AHS Air International: 1 freight (AP-BIO)
Cargo Air Lines: 1 combi (4X-ICM)
Caspian Airlines: 1 freight (EP-CQA)
Iran Air: 3 passenger (EP-IAG, EP-IAH, EP-IAI), 1 combi (EP-ICD)
Jet Star: 1 freight (ER-BBS)
Kabo Air: 3 passenger (5N-DKB, 5N-JRM, 5N-MAD)
Kalitta Air: 2 passenger (N715CK, N793CK), 4 freight (N704CK, N746CK, N794CK,* N795CK*)
Kam Air: 1 freight (4L-TZS)
Midex Airlines: 3 freight (A6-MDG, A6-MDH, A6-MDI)
Orient Thai Airlines: 1 passenger (HS-UTC)
Rayyan Air**: 2 freight (AP-BKI, AP-BKS*)
Saha Airlines: 2 freight (EP-SHB, EP-SHH)
Saudi Arabian Airlines: 1 freight (HZ-AIU)
United States Air Force: 2 VC-25A (82-8000, 92-9000)
Uni-Top Airlines: 3 freight (B-2448,* B-2450,* B-2462)
Veteran Avia: 1 freight (EK74799*)
Vision Air International: 1 freight (AP-BIV)


* Built as passenger and converted to freight.
** Not to be confused with Ryanair! :-)

There are also several stored aircraft, including the Rolls-Royce test plane you mention in the question.



Thanks to fooot for explaining that BSF denotes "Boeing Special Freighter", a passenger plane converted to freight use.