1. A method, performed by a computing device having a memory and processor, for identifying targets of interest within captured image data, the method comprising: receiving, from a user, a selection of a first portion of a first frame of image data, the first portion of the first frame of image data including a target of interest; determining a characteristic value for each of a plurality of pixels within the selected first portion of the first frame of image data; generating a first series approximation for the characteristic values of the plurality of pixels within the selected first portion of the first frame of image data based on pixels only within the selected first portion of the first frame of image data; generating a target signature for the target of interest based at least in part on the generated first series approximation; and for each of a plurality of second portions of second frames of image data, determining a characteristic value for each of a plurality of pixels within the second portion of the second frame of image data, generating a second series approximation for the characteristic values of the plurality of pixels within the second portion of the second frame of image data, generating a comparison signature for the second portion of the second frame of image data based at least in part on the generated second series approximation, and determining a difference between the target signature and the comparison signature generated for the second portion of the second frame of image data.