Adult vs Juvenile

It's pretty impossible to differentiate between the male and female Lineated Barbet, and also the juvenile or sub-adult and the adult.  Having watched the birds and going through some images taken over a period of five days finally gave me some confidence to make a comparison between the adult and the young, in terms of colours and features like the eyes and the bill.
The two following images are pretty easy, the adult image was taken in October 2017, and the young from recent days.

I've also tried to compare them by poses, which will ensure accuracy, and fortunately these were taken on the same day.

Adult

Juvenile

Juvenile

Adult

Juvenile

Adult

Juvenile

A couple more images and here it's not difficult to make out the differences.

Adult

Juvenile

Adult