The main purpose of the badge was to identify the individual quickly, particularly denoting their rank, thus allowing all servicemen to respond according to the rules should they meet a higher, equal or lower rank. Eventually though, the badges were soon found to be impractical in the trenches as anything shiny could glint and attract enemy attention, so the badges were removed and cloth versions issued. Everyone in service had a badge issued and because they were obvious souvenirs many survive today.
Studio photographs had to be purchased by the sitter and it is important to remember that a photograph in the albums or papers of a relative is not necessarily a portrait of them. It was common for soldiers to swap photographs with their friends as souvenirs, and most soldiers wallets contained photos of friends as well as relatives, not usually their own.
When looking at photographs some badge designs relate to the function of the corps or regiment that the badge belongs to. For example, on the Royal Artillery cap badge a gun is incorporated into the design. The badge overall is a distinctive triangular shape, and can often be easily identified, even in a blurred photograph. However, some units had very similar cap badges which can be hard to differentiate.