I think the key is intent - call it the Reasonable Man test - would a reasonable man think you are trying to dodge the system ?
Buddy : Hey rudy, can you go take some pictures of my house ?
Rudy : Sure Buddy.
<zoom zoom click click zoom zoom>
Rudy : Here ya go - pictures !
Buddy : Cool - here's some cash
Wah Wah Ooops. You flew with the intent of taking the pictures, you are essentially a charter (The pictures were the reason for the flight), and certainly commercial, especially when you accept the money.
However :
Rudy : Hey buddy, See these pictures I took yesterday on the way to breakfast ?
Buddy : Hey Look ! Thats my house ?
Rudy : Really ? I didn't know that ! Nice pool !
Buddy : Can I have it ? - here's $10 for the ink and paper and stuff
Rudy : Well cool - can't accept the money tho - only cost me $100 to go to the breakfast anyway.
Buddy : Well, I insist - in fact, here's $50 to cover half your flight expenses.
Rudy : Well, next time we go to Podunk for breakfast, I'll let you know and you can come along and bring your camera
Still commercial ? Maybe, but it was never the
intent. The FAA may look on it as Goodwill, or even compensation, but if I give a confused student the right frequency while flying in another plane, I get goodwill...doesn't mean I need a CFI ticket. If Buddy had been in the plane at the time and taken the pictures, and paid half the expenses for the original breakfast trip, noone would even bat an eyelid. The purpose of the flight was always BREAKFAST - the photos were incidental.
Obviously, if you 'go to breakfast' every day and have twenty five 'buddy's whose houses you knew were on the way....
Rudy said:
The other day one of my dad's friends wanted some pictures of the city of Pittsburg so me and my brother went up and took them.
In this case, I think you are a whole lot closer to the first example than the second. The reason you went flying was to take the pictures. Thats a commercial endeavour (whether you get paid or not).