How to implement 'the angel of uncertainty'?

[Lefteyeshooter]

I got inspired by this Sally Mann video, in which she talks about the importance of dust and scratches in her collodion glass plates. Because of the random, unpredictable nature of it, she calls it the 'angel of uncertainty'. The video is here: https://www.nga.gov/audio-video/video/mann-colldion.html 

Here is an example of such a picture: https://www.nga.gov/collection/art-object-page.161961.html 

I wonder if there is a way to implement this in the digital age using Affinity Photo?

 

[Medical Officer Bones]

Many, many ways to introduce randomness in you work. One obvious method is to scan in or digitally photograph a sheet of paper that you've dirtied up and treated somehow, and combine that in your work with various layer blend modes and masking. A simpler method would be to download one of the multitude of free "dirty" / "scratches" / etc. brushes from the net, and combine them in your work.