THERE are about 300,000 row houses in Philadelphia, which means there are about 300,000 row house owners in Philadelphia who would like to see their tax assessments lowered.

Some of them get in touch with the city’s Board of Revision of Taxes. A caller may say, “Our house is in the worst condition of any on the block,” said Barry Mescolotto, the board’s assistant administrator.

These days, Mr. Mescolotto has a good answer: “I’ll say, ‘I’m looking at a photo of your house, and it looks to be about the same as all the others.’ ”

“That usually ends the conversation,” Mr. Mescolotto said.

Until recently, assessors had to accept homeowners’ claims or visit the properties themselves. But in 2003, the city hired the Pictometry International Corporation, a company in Rochester, N.Y., to provide images of every building in the city.