What is it?
If you want to run analytics on images then you need to have the images to analyse. This process is therefore the dedicated collection of useful images for that purpose.
With the increase of social media platforms and smartphones there is now an abundance of images that could potentially be useful for analysis.
Why does it matter?
Image data matters because a picture paints a thousand words and that is still true. There is a huge amount of information that can be gleaned from a photograph or image above and beyond what is contained in the image. For example, photographs have GPS-based meta-data that will tell you when the photograph was taken as well as where the photograph was taken.