What's wrong with the picture to the left?
In all DWI cases where the defendant is expected to submit to the Alco-Test (or breath test) to determine blood alcohol content, the arresting officer must be able to testify that the accused did not place any foreign substances into his or her mouth.
Cuffing a defendant in the front makes it increasingly difficult for an officer to testify with certainty that nothing was placed in the mouth for a period of 20 minutes before submission to the Alco-Test. Because, of course, the hands can reach the mouth.
Most officers know this, and are also trained to restrain the accused with the hands placed behind the back for safety reasons. However, mistakes and exceptions are made. Exceptions usually apply to obese defendants or those that have health issues.
Unless a person arrested for DWI is cuffed in the rear, the state may have difficulties in establishing standards for the admissibility of the Alco-Test reading.