Warm filters, higher contrast and increased exposure boost both views and comments, according to new research into user engagement by Yahoo Labs and Georgia Institute of Technology.

Filtered photos are 45 per cent more likely to receive comments and 21 per cent more likely to be viewed, with warm filters significantly boosting comments and increased exposure most strongly influencing views.

On the other hand, ageing effects lift views slightly but decrease comments, while saturation effects boost comments but have little influence on views, the study found.

All these effects were observed after taking into account follower count and photo stream popularity.

"In colour theory, warm colours such as red and yellow are known to elicit feelings of arousal and cheerfulness, and our results seem to echo this," the authors wrote.

The study of 7.6 million Flickr photos, more than half of which were cross-posted from Instagram, also examined people's motivations for choosing filters.

Unsurprisingly perhaps, casual photographers are primarily motivated by the act of sharing and use filters to dramatically transform their photos.

Serious photographers, on the other hand, use filters to correct errors or highlight features and regard the image itself as the most important, the authors found.

The paper is the latest in a growing body of research into the use of images on social media.

The popularity of selfies among viewers was also confirmed by the same authors in a 2014 study which found photos of faces rather than places attracted the highest engagement.

Their analysis of 1.1 million Instagram images found photos with faces were 38 per cent more likely to receive likes and 32 per cent more likely to receive comments, after controlling for social network reach and activity.

However, the number of faces, their age and gender had no effect, according to the study.

"We are social animals and want to see other people — it's comforting to us and makes us safe," according to lead author Saeideh Bakhshi from Yahoo Labs. "This is engrained in us at a very early age, when babies are looking for the support of their parents."

Other research from Arizona State University found the five most popular Instagram filters are Normal (unfiltered), Amaro, X-Pro II, Valencia and Rise.

However, the authors of the 2014 study of more than 5.6 million images also noted that these five filters appeared among the first seven options in the Instagram interface, so perhaps user choices were driven more by convenience than creative impulse.