Mr Grant was driving on the Newell Highway in rural NSW on Saturday when he stopped for road works and snapped the picture of a ewe, which was in the boot of the car ahead of him.

He later posted it to Twitter.

"Heading home on the Newell stopped at upgrade works and then saw this. A ewe in the back out on a Saturday drive!" he wrote.

The National Party MP was left sheepish when a journalist asked if it had been taken from the drivers' seat, and he admitted it was.

When Mr Grant was informed that what he did was illegal, he contacted police to dob himself in for a $325 fine and four demerit points.

In an interview on Sydney radio station 2GB on Tuesday, Mr Grant said his car was turned off at the time, and his phone was in a cradle attached to his air conditioner vent.

"[I'm] $325 lighter in the pocket, paid it this morning," he said. "When you do the wrong thing and it's brought to your attention, you've gotta to the right thing and cop it on the chin like everyone else.

"Yes, I was behind the wheel."

Mr Grant said he used his phone to capture something "which was a bit unusual and I thought was funny" and didn't remove his phone from its cradle.

"I just quickly took the photo. Eventually we took off and I got home and posted it after I got home," he said.

"That's how it worked, but it's obviously an offence and when I became aware of that I owned up to it, rang the police and asked them to send me the bill, and I received it and paid it this morning.

"Obviously if I knew it was an offence I wouldn't have posted it on social media or taken the photo. We all make mistakes ... it's a message that no one's above the law."

Mr Grant said he wouldn't be repeating the mistake.

"I've paid the price, but I hope everyone else has learned the lesson."