I think you are confusing the definition of rent seeking, meaning achieving economic gains by means of regulation that is virtually risk free, with collecting rent as a form of payment for a service or product. These are two different concepts, despite the name they share.
"rent seeking", in economics, is not limited to regulation. We would distinguish between those who earn money by creating new value - as the inventor makes some process more efficient, and so makes his living - and those who earn a living despite creating no value. The easiest example of this is the man who has inherited some plot of land, and rents out the plot to someone. He might earn a healthy living - but where has he created value? The strongest example of this is perhaps he who earns money by destroying value - say the window repairman who goes out at night and smashes windows - but this is not required to be classed as rent seeking.
Photoshop, being nearly a monopolist, seems to almost fit the definition. Regulation is the only thing here that doesn't match, but being a de facto industry standard would be close enough for me.