We developed invisible code that is suitable for embedding into a natural image. Our code consists of a background layer, color adjustment layer and code layer. The code layer is composed of edgeless high-frequency blocks and edgeless low-frequency blocks. Two key technologies were devised to implement this idea. One is the color adjustment layer that adjusts the color of the background image for high-frequency blocks using an original blur filter. The other is the edgeless high-frequency block that increases the transparency of the periphery of the high-frequency block. To verify the effectiveness of our invisible code, we estimated the invisibility and reading accuracy for code embedded in four common types of images. The results demonstrate that the invisibility has been improved about 1.34 times and the reading accuracy has been improved about 1.38 times compared with the conventional invisible code.