Babysitter rapist Alan Webster had his "unduly lenient" minimum jail term of six years increased by two years by the Court of Appeal today.
But his co-accused Tanya French escaped an increase in her original five-year custodial sentence.
The pair carried out sexual offences of the "gravest depravity" against a 12-week-old girl.
A panel of five senior judges, headed by the Lord Chief Justice, Lord Phillips, ruled that Webster's six-year minimum term - the least he has to serve before he can be considered by the parole board for release - was too short.
But Lord Phillips stressed: "His sentence was life imprisonment and such was his depravity that it was questionable whether the parole board would ever consider that he should be released."
The court ruled that having regard to French's youth and the fact that she had been corrupted by Webster, her sentence fell within the range that was properly open to the sentencing judge "and should not be disturbed".
They had been urged to raise the length of the original sentences by the Government's senior law officer, Attorney General Lord Goldsmith QC.
Lord Goldsmith said the crimes committed by Webster and French had "shocked and outraged public opinion".
Webster, 40, and French, now 20, of Hatfield, Hertfordshire, raped and indecently assaulted the baby and took photographs of the abuse.
Webster was jailed for life in January after pleading guilty to rape, indecent assault, permitting indecent images to be taken of a child and making indecent images.
A judge at St Albans Crown Court set a minimum term of six years in Webster's case - meaning he must serve at least that amount of time behind bars before he can be considered for parole.
French was jailed for five years and given an extended licence period of five years after admitting the same charges.
The baby's mother has described the sentences given to the pair as a "joke".
She was unaware of the abuse until detectives visited her after finding photographs detailing the horrific abuse at Webster's home.
Webster, described as "evil and depraved", also pleaded guilty to a separate charge of indecently assaulting a 14-year-old girl.
At a recent hearing Lord Goldsmith said he was asking the court to review sentences imposed for "offences of the gravest depravity against an innocent defenceless baby and another young girl".
Lord Goldsmith said the cases of Webster and French were "exceptional in the nature of what took place and their depravity".
He told the judges: "You may think that, having seen the photographs, that what took place was almost beyond comprehension.
"The acts of those two offenders will have done incalculable damage to the baby and her mother."
Lord Phillips said the pair had carried out a course of conduct "of horrifying depravity" in which they "used a baby girl, entrusted to the care of French as a baby-sitter, as a sex toy".
Webster first met French when she was 14, but their close relationship began when she was 17.
Lord Phillips said she moved into his home and it was clear that he corrupted her, so that she was "fully complicit" in the offences.
At the time of the offences French was aged 17 or 18.
She had become friendly with the baby's mother, said the judge: "French used to baby-sit and on occasions the mother permitted French to take the baby to Webster's home to look after her there.
"This enabled Webster and French to plan the offences that they carried out on the baby."
The evidence "did not establish more than a possibility that the baby's treatment will result in long term psychiatric damage, but there is a risk of this and it should have been apparent to the offenders that there was a risk that they might cause the baby long lasting psychiatric injury".
Lord Phillips said: "There is an obvious possibility that, when she grows up, the baby will discover from someone what was done to her in the early months of her life and that this may cause her psychiatric harm.
"In a witness impact statement the baby's mother spoke of the acute distress that she experienced as a result of being told by the police what had been done to her baby daughter.
"She described the occasion when she learnt this as the worst night of her life, worse even than an occasion some years earlier when she was the victim of rape. We have well in mind the effect on the mother of learning of the offences."
The judge stressed that Webster's life sentence meant that he would remain in prison "unless and until the parole board is satisfied that he no longer poses a danger to the public".
He added: "The evidence in this case shows that he is so deeply steeped in sexual depravity that it is questionable whether that day will ever be reached."
The offending combined the "aggravating features of repeated rape of a victim over a period of time, breach of trust and rape of the most vulnerable victim possible - a tiny baby.
"It was this last feature which produced the understandable and justifiable public revulsion."