"The data was photographed from a (computer) screen and pieced together bit by bit," lawyer Jorg Schauf, representing a UBS client, told the Tages Anzeiger.
Describing the quality of the information obtained by the German state of North Rhine-Westphalia as "remarkable", Schauf blamed the "work of an internal source" for the leak.
Many banks have worked to shore up internal security protocols since client's private information began to find its way to German tax investigators in 2007, which this latest method circumvents.
"Everything is in (the photographs)," said Schauf, including a complete overview of clients' assets, their wealth before and after the global financial crisis and the names of their advisers at the bank.
The data handed over contains information on assets worth more than Sfr3.5 billion (€2.9 billion), with the most recent information dating back to March 2010, the daily reported.
New procedures are being introduced at the bank, a UBS spokesman said.
A tax deal between the two countries aimed at ending such exchanges is proving elusive after Germany's upper house -- the Bundesrat -- blocked ratification last month.
Under the terms of the double taxation agreement signed by ministers from both countries earlier this year, German citizens with assets parked in Switzerland's notoriously secretive banks faced paying a tax rate of 26.4 percent on their holdings.