A mura defect detection algorithm for thin-film transistor liquid crystal display (TFTLCD) is developed for automatic detection of mura defects using Discrete Cosine Transform (DCT) principle for background image reconstruction. Detecting blob-mura defects in a LCD panel can be difficult due to non-uniform brightness background and slightly different brightness levels between the defect region and the background. To resolve this issue, a DCT-based background reconstruction algorithm was developed to establish the background image. The background of the inspected images can be first extracted and reconstructed by using the DCT principle and an image filtering strategy. Mura defects can then be detected by the developed segmented strategy. Actual performance of the developed method was evaluated on industrial LCD panels containing natural mura defects.