Camouflage is a classic example of the power of natural selection. While the general benefits of camouflage are apparently obvious, understanding the precise means by which the viewer is fooled represents a challenge to the biologist, because camouflage is an adaptation to the eyes and mind of another animal. A goal of my project is to understand cryptic defence, and its relationship with the background. In this study, moths, both real and artificial, were used as a model of cryptic camouflage in order to understand untested theories of protective colouration in animals; additionally, to evaluate whether the results generalize across birds and humans. Chapter 1 provides a brief review of the existing literature in the field, starting with all the recognised types of camouflage and the general principles of them for minimising detection; human, avian and insect vision science are reviewed in relation to object detection and pattern discrimination. Chapter 2 is an introduction to the visual systems of the animals involved in this study, including human, birds and insects. Due to the differences amongst them, we cannot investigate and measure colour and pattern by using human vision as the standard; therefore the other section in this chapter is the methodology of digital image analysis that relates to these visual systems. Chapter 3 is an investigation of the factors that influence visual search, by birds and humans, for camouflaged objects against natural complex backgrounds, including similarity in colour and luminance, and so-called 'feature congestion' in the immediate background: rapid colour and luminance changes, and variation in orientation of relevant and irrelevant items. Chapter 4 is an investigation of how important patterns (textures) with lower or higher spatial frequencies, on objects of different sizes, are for concealing them on natural backgrounds. Chapter 5 tests whether the previous conclusions regarding camouflage really are the case in the real world, by analysing the patterns of real moths in relation to the backgrounds they are sitting at. Chapter 6 comprises general conclusions on what we have learnt from the research in this thesis and priorities for future investigations.