1. A method performed by a computing system for identifying objects within a medium, the method comprising: accessing a sequence of image frames of the medium, each image frame corresponding to an along-medium location, each image frame corresponding to an along-medium location having, for each of a plurality of depths and for each of a plurality of cross-medium locations, a voxel at that depth and at that cross-medium location, each voxel having an intensity; generating a depth-compensated intensity for each voxel that is a normalization of the intensities to account for variations resulting from differences in depth such that, for each depth, the depth-compensated intensity for a voxel at that depth is based on the intensity of the voxel and statistically derived characteristics of the intensities of voxels at that depth; and analyzing the depth-compensated intensities to identify cross-medium locations of image frames with object voxels that represent part of an object.