Image authentication techniques have recently gained great attention due to its importance for a large number of multimedia applications. Digital images are increasingly transmitted over non-secure channels such as the Internet. Therefore, military, medical and quality control images must be protected against attempts to manipulate them; such manipulations could tamper the decisions based on these images. To protect the authenticity of multimedia images, several approaches have been proposed. These approaches include conventional cryptography, fragile and semi-fragile watermarking and digital signatures that are based on the image content. Some of the researchers proposes image authentication with data repair capability but these techniques only work for specific category of image. A new authentication method based on the bit plane slicing with a data repair capability for grayscale image, grayscale document image, color image and color document image is proposed. In this proposed technique alpha channel is used for embedding authentication data. In Portable network graphics (PNG) image alpha channel is already present but for other image formats alpha channel additionally combined with cover image. An authentication signal is generated using Binariation from cover image and embedded into an alpha channel plane. The alpha channel plane is then combined with the original grayscale image to form a PNG image. During the embedding process, the computed authentication data are mapped into a range of alpha channel values near their maximum value of 255 to yield a transparent stego-image with a disguise effect. In the process of image authentication, an image block is marked as tampered if the authentication signal computed from the current block content does not match that extracted from the content embedded in the alpha channel plane. Data repairing is then applied to each tampered block by extracting authentication data from alpha channel plane. Measures for protecting the security of the data hidden in the alpha channel are also proposed. Good experimental results prove the effectiveness of the implemented method for real applications.