1. A system comprising: first means for receiving a query for a particular action, wherein the query includes a query video; second means for computing motion similarity between a first group of pixels in a first frame of the query video and a second group of pixels in a second frame of a video via one or more motion vectors in the query video and the test video; third means for providing one or more similarity values in response thereto; forth means for aggregating the one or more similarity values, yielding one or more aggregated similarity values in response thereto; fifth means for using the one or more similarity values to estimate where the particular action or version thereof occurs in the test video; sixth means for estimating optical flows associated with the one or more motion vectors; and seventh means for computing a confidence score for the particular action based on the aggregated similarity values, wherein the confidence score (C(i)) is computed in accordance with the following equation: C ⁡ ( i ) = max max ⁡ ( i - T / 2 , 1 ) ≤ k ≤ ( i + T / 2 , Ttest ) , 1 ≤ j ≤ Tquery ⁢ S a ⁡ ( k , j ) , wherein Tquery represents a number of frames in the query video; Ttest represents a number of frames in the test video or portion thereof; k is a frame counter corresponding to a given test frame; i is a counter corresponding to a given test frame; j is a counter corresponding to a given query frame; C(i) is a confidence score for a T-length space-time (ST) region centered at frame i of the test video; and S a (k,j) is an aggregated similarity value estimating how similar a T-length video centered at frame k of the test video is to a T-length video centered at frame j of the query video.