The maximum sentence for the offence to which Venables pleaded guilty is five years. Below is an extract from the sentencing guidelines for the offence:
• Sentences up to the statutory maximum should be imposed when there is a contested case and there is evidence of commercial or large-scale exploitation and there is a significant amount of material, especially if the offender has previous convictions.
So it is unlikely that the judge considered that the maximum was warranted (there was, as far as I know, no evidence of commercial gain, and fifty-seven images is a small number when compared to some cases that come before the courts.
Since he pleaded guilty at the earliest opportunity he is entitled, by law, to one third off any sentence which would have been handed down had he been found guilty at trial, thus making the maximum available t the judge three years and four months.
The two years he received equates to a three year sentence before discount and I would suggest that, based on this case and bearing in mind his background, it might be a tad light, but not excessively so.