Factors affecting the accuracy of using digitised images of projected particles in order to determine particle properties such as shape, size and particle perimeter are defined. In particular, the inaccuracies in the representation of particles of known shapes as digitised particles under different resolutions due to loss of information at the particle boundary are quantified. The results are generalised for arbitrary shapes by the use of mathematical proof and implications are considered for relevant particle analysis techniques. An attempt is made to find relationships between resolution and accuracy, and between particle shape and accuracy. Accuracy here is defined as the deviation of the area of the digitised image from the actual area of the real particle. Implications for accuracy of 3D digitised representations of particles are highlighted and its relevance to predictions of 3D particle packing based on the digitised data.