1. A method comprising: determining, via a computing system, traversing content in a set of images based on a comparison between a background model of the set of images to image data representing the set of images; using a target content model to determine target content in the traversing content; and generating a composite image by replacing the target content with different content, wherein generating the composite image includes: segmenting the target content from the set of images based on a model of the set of images as a mixture of at least two image layers, wherein one of the least two image layers includes components of a foreground corresponding to the target content and the other of the at least two image layers includes components of a background corresponding to content of the set of images other than the target content; determining an initialization map that identifies a first region of the set of images corresponding to the foreground and a second region of the set of images corresponding to the background; deriving from the initialization map an alpha matte specifying respective contributions of the at least two image layers to the foreground and to the background; and performing a weighted blending of replacement content into the set of images in accordance with the alpha matte.