Comets are the primitive building blocks of the Solar System. In order to understand the extent of the pristine nature of comets, we must understand the mechanisms that affect their surfaces and comae -- their activity. Activity can be tracked in a variety of ways, such as observing dust production in the coma using broadband imaging. Activity varies from comet to comet so we must try to distinguish whether these differences in activity are because of ageing or reflect primordial differences. Ageing refers to effects that have chemically or physically altered the nucleus since its formation and cause a change in the activity. I developed a pipeline to calibrate and measure broadband photometry of comets in a consistent way. The pipeline calibrates the brightness to a common photometric system using background stars in the field. I applied this pipeline to ground-based data accompanying the Rosetta mission. The photometry of 67P followed the predictions based on previous apparitions: it showed no obvious change in activity levels from orbit-to-orbit and coma colours remained constant throughout the apparition. I detected an outburst on 2015 August 22 of ∼0.14 mag. The brightness and estimated mass of this outburst put it in line with the outbursts directly observed on the nucleus by Rosetta. An in situ outburst was observed at the same time as the one seen from the ground; however, linking these two events directly remains challenging. I applied the pipeline to TRAPPIST photometry of 14 comets. I determined that comets of different dynamical classes can be distinguished by their dust activity: dynamically new comets displayed higher dust production rates and greater asymmetries in the dust production rates about perihelion than other comets. There seemed to be no correlation as to whether the peak of activity occurred before or after perihelion. I found strong relationships between dust and gas production which can be used as a rough approximation of gas production rates if one is only presented with broadband data. I found that a decrease in V− R colour is strongly correlated with an increase in gas production pre-perihelion
