Knuckle Down ID is part of a three year PhD project, assessing human variation in the knuckle creases on the back of the fingers and the impact of finger bending on their appearance in digital images. The images collected through this citizen science project will be used to develop a suitable AI algorithm to replicate the process of identifying perpetrators from digital images using knuckle creases.  Instructions You will be asked to complete a questionnaire and then take images of your hands positioned around a round cup or mug with a smartphone through the Knuckle Down ID app. Image collection will be guided through the app and examples will be provided. Throughout this app you will be asked questions regarding your age, sex and which hand is your dominant hand. You will also be asked to upload images of your hands. The organisation of data collected by the app is addressed in the initial information pages of the app and permission is requested to use the data for a study.