Content aware image resizing technique has become more important with the development of device technology. Although the seam carving method produces high-quality resized images, it requires high computational complexity. In this paper, we propose a block-based seam carving method, which is extended from the seam carving method. In our method, a seam element is a pixel block, and a seam is a path of blocks. The blocks on a seam are downsampled in the step of image shrinking. Our method creates resized images with less distortion and runs faster than seam carving. In addition, we present an image magnification technique with our method. Unlike the seam carving method, our technique defines the optimal seam for enlargement. Simulation results show the advantage of our method over seam carving method.