The appearance of the upper bubble surface of a flotation froth is used qualitatively as a basis for control in industrial flotation cells. The complex structures that constitute the surface of a froth are indicative of the sub-processes occurring within the froth, and which affect the flotation performance. Being able to accurately and automatically measure bubble size and shape distributions is therefore an important requirement for the optimisation and control of froth processes. An algorithm has been developed for froth surface bubble size distribution measurement, and that is largely insensitive to factors such as froth type, lighting conditions and bubble size. In this algorithm, reconstruction is applied following the subtraction of a constant value from the image. Regional maxima are identified and used as markers for the watershed, which segments the image. Equivalent circular bubble size and shape distributions can be determined from the number of pixels in each segment. It is shown that the bubble segmentation algorithm can be generally applied to flotation froths from a variety of minerals and conditions, and may be suitable for application in automated industrial froth characterisation and control systems.