A report from the Public Accounts Committee has shown that nearly half of all photographs taken by garda speed cameras were useless.
The figures are contained in a study of the penalty points system.
The committee undertook an analysis of the penalty points system as part of its examination of the Department of Justice Equality and Law Reform.
Its figures indicate that of over 100,000 photos taken by fixed cameras, just under half were defective.
The PAC study also found that while just over 50% of those on whom on-the-spot fines were imposed paid up, only one in seven of the remainder were successfully pursued through the courts.
It is likely that the PAC report will find that the effectiveness of the penalty points system has been seriously eroded by administrative inefficiency.
The report comes as the Road Traffic Bill 2006, which provides for more speed cameras and extends the penalty points system, is being debated in the Dáil.