Baltimore lawyer William H. "Billy" Murphy Jr. said he's looking at such issues.

"We're taking it very seriously," he said. "A suit would be extraordinarily popular and extraordinarily important. We've got to put machine justice in its proper place."

Baltimore City and the surrounding counties with speed cameras all pay their camera contractors a per-ticket fee, flouting a section of Maryland's speed camera law that was designed to prohibit such "bounty" arrangements. Gov. Martin O'Malley said earlier this month that he thinks state law bars the practice of paying contractors based on the number of citations issued or paid.

Lande said the plaintiffs could try to overturn the camera system on that basis alone. Counties have argued that their contracts are acceptable because the law addresses private "operators," and the governments consider themselves the cameras' operators.

Xerox's admissions about errors, combined with the per-ticket payout plan, would give a plaintiff's attorney enough ammunition to argue that the whole speed camera system is unfair, Lande said.

But to have the best chance of success, Lande said, he thinks the plaintiffs would need to show that the cameras are inaccurate. And to do so, attorneys would have to get hold of the cameras' raw data to work out exactly how unreliable the devices are. That prospect is complicated by a state law that bars release, without a driver's permission, of the cameras' photographs — the very evidence needed to confirm whether tickets issued by the camera are valid.

"Only if the plaintiffs were very well-financed and determined would they have a chance of collecting the necessary evidence," Lande said.

And even then, should the plaintiffs win their case and get the tickets reversed, they would be unlikely to prove that drivers suffered damages beyond their $40 outlay, and thus were entitled to anything but a refund, Lande added.

Attorney Timothy P. Leahy has sued speed cameras in Montgomery County without success — after a state appellate court ruled he didn't have standing. He is trying a new legal argument against a Prince George's County system, with a $5 million class action suit in which a police officer alleges that the government forged his signature on speed camera tickets. In that case, Leahy is using the argument that his clients have standing as taxpayers.

If he is successful there, Leahy said, he plans to expand the suit against speed cameras to possibly include Baltimore and other jurisdictions. He said he's trying in Riverdale Park because he has "evidence of outright fraud" there.

Even though his Montgomery County suit was unsuccessful, Leahy said he believes he can prove that paying vendors per citation is illegal, if he can just establish standing.

"If even the governor admits these [contracts] are illegal, why are they continued to operate this way?" Leahy said.