White paper: The impact of images on the engagement of posts published by French media on Facebook

Following the results of two studies conducted in September 2019 by Nonli's Data Science team on engagement excluding clicks on Facebook (reactions, comments and shares) of type link and photo posts published during the 2nd quarter of 2019 on the pages of 133 of the most important French media in terms of web traffic (PQN, PQR, Magazines, TV, radio), we have decided to condense the results.

The fact that this document focuses particularly on Facebook publications is justified by 2 main elements:

- the #1 social network in France is Facebook with 27 million daily active users,

- Facebook is the social network on which the media are the most active and through which they directly generate web traffic and revenue.


The impact of images in type link posts

Image resolution

Images of type link content are standardized and often go through an adjustment between the original URL and Facebook.

Among the media publications analyzed, we find three raw image formats distributed as follows:

- 5% are square, 

- 88% are in landscape format 

- 7% are in portrait format.


We have classified the images into two categories: 

- small images with a resolution of less than 500 pixels in width or height,

- large images with a resolution of 500 pixels or more in width or height.


Screenshot 2019-11-13 at 11.10.31


Engagement in relation to image resolution

The graph below shows that large images have a median engagement that is twice as high as small images (174 vs. 89). And since 92% of the images considered are large, the median evaluated for all images is almost equal to that reached by large images.

It therefore seems more interesting to focus on images with high resolutions to avoid transformations made by Facebook that could degrade the image and weaken its engagement potential - especially since small image formats often result in mobile formats with an image placed on the left and the title and description placed on the right, and where the image is made less visible and therefore less engaging.

In an effort to identify an ideal format, we wanted to identify the resolutions beyond which the engagement did not evolve or only slightly, and as can be seen in the second graph, there is no ideal format - on the other hand, the resolution of the raw image must not be less than 400 pixels wide or high depending on the image format, at the risk of experiencing a negative impact on the engagement.




Engagement in relation to image formats

We also wanted to define which formats, among large images, were the ones that corresponded to the most engaging posts.

To do this, we decided to exclude from our analysis certain rectangular formats that are visually close to the square format in order to avoid any bias from this point of view - in this case those whose difference between width and height was less than 20%.

The engagement results are as follows:

- landscape format: 187 median engagements per post,

- portrait format: 109 median engagements per post,

- square format: 56 median engagements per post

The landscape format therefore seems to be the one to prefer when publishing type links since it engages 1.7 times more than vertical images and 3 times more than square images.



The impact of images in type photo posts

Image formats and resolutions

7% of publications over the period were type photos versus 85% of type links. 

Among the type photos, the distribution of formats is as follows:

- 34% of square images,

- 37% of landscapes,

- 29% of portraits.

The resolutions, whose format distributions are displayed below, range from 100 to 720 pixels wide or high, which is much lower than for type links, although in their case small images (less than 500 pixels wide or high) are also rarely used - only 0.8% in the case of type photos.

It should also be noted that in more than 80% of cases, the resolution is 720 pixels in x or y for all three formats.



Engagement in relation to the image formats

By following the same methodology as for type links and only taking into account images with a difference of at least 20% between width and height for rectangular images, we can see that for type photos, it is the square format that engages best, ahead of portrait and landscape formats.

It should be noted that the order is the opposite of that of type link posts and that there is a gap of about 154% between square images and landscapes.




Among all the publications of the second quarter of 2019, several things can be observed after analysis:

1. The most engaging type link posts that contain an image are those whose image resolution exceeds 400 pixels.

2. The images used for type link posts have a higher resolution than type photo posts - this can be explained by the use of higher quality photos on the websites of the media studied. Facebook recommends using photos that are 720 pixels, 960 pixels or 2,048 pixels wide, so it seems that in the case of type photos, the resolutions of the downloaded images chosen are less than or equal to 720 pixels.

3. Landscape images are much more numerous than other formats in type link publications and are the most engaging.

4. On the other hand, for type photos, there is no privileged format, although the images related to the most engaging publications are in square format, and to a slightly lesser extent in portrait format.

Our recommendations are as follows:

- prefer high resolution images for all types of posts,

- for type links, choose images in landscape format,

- for type photos, use square and portrait formats.