The Ministry of Justice has said it will take "immediate action" after claims that a jailed hit-and-run driver used social media in prison.
It follows a newspaper report claiming that Aidan McAteer celebrated his 24th birthday by posting an image of a card on Instagram which appears to be from fellow inmates.
He is called HMP Birthday Boy in the card.
The Liverpool Echo said the post, which has now been removed, is among several images published by McAteer since he was jailed in May over the death of four-year-old Violet-Grace Youens.
McAteer was sentenced to nine years and four months after the stolen vehicle he was driving more than 50mph over the speed limit hit Violet-Grace and seriously injured her grandmother Angela French in St Helens in March.
McAteer, who pleaded guilty to causing death by dangerous driving and causing serious injury to Ms French, had run past Violet-Grace as she lay injured on the ground following the crash.
A Prison Service spokesman said: "This behaviour is completely unacceptable and we are taking immediate action.
"We are clear that those who break the rules will be punished and can face extra time behind bars.
"We are taking decisive action to find and block mobile phones in prison, including a £2 million investment in detection wands and legislation to block phones from being in prisons."
Bringing a mobile phone into prison or transmitting sounds or images from within a prison using a mobile phone can carry a maximum sentence of two years in prison.
Prison officials are investigating the matter.