This dissertation develops a novel system for object recognition in videos. The input of the system is a set of unconstrained videos containing a known set of objects. The output is the locations and categories for each object in each frame across all videos. Initially, a shot boundary detection algorithm is applied to the videos to divide them into multiple sequences separated by the identified shot boundaries. Since each of these sequences still contains moderate content variations, we

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... use a cost optimization-based key frame extraction method to select key frames in each sequence and use these key frames to divide the videos into shorter sub-sequences with little content variations. Next, we learn object proposals on the first frame of each sub-sequence. Building upon the state-of-the-art object detection algorithms, we develop a tree-based hierarchical model to improve the object detection. Using the learned object proposals as the initial object positions in the first frame of each sub-sequence, we apply the SPOT tracker to track the object proposals and re-rank them using the proposed temporal objectness to obtain object proposals tubes by removing unlikely objects. Finally, we employ the deep Convolution Neural Network (CNN) to perform classification on these tubes. Experiments show that the proposed system significantly improves the object detection rate of the learned proposals when comparing with some state-of-the-art object detectors. Due to the improvement in object detection, the proposed system also achieves higher mean average precision at the stage of proposal classification than the state-of-the-art methods.