It sounds to me like a carriage-return carriage-return/linefeed problem which is not visible in your text files, but destroyed the contents of image files.

Are the source and destination different types of computers, i.e. Windows and Linux? Did you transfer the files first with FTP to a Windows computer and then back to a Linux computer? Was with one of those transfers ASCII mode in FTP selected?

You can first uncompress the tar file with gunzip, and then extract the resulting tar file with tar xvf.