Starting with WinImage 6.0, you can encode .WLZ and .IMZ files with a password.
When you save a .WLZ or .IMZ file, you can enter a password. WinImage will encrypt the image file with this password. This password will be required for opening these files later.
WinImage use MD5 algorithm ( http://userpages.umbc.edu/~mabzug1/cs/md5/md5.html ) to build a 128 bits keys from password, and then the new Rijndael encryption algorithm
You can create Self-Extracting EXE file with encrypted file. Of course, this executable will prompt the user for a password.
Before sending encrypted file on the Internet, check that your country laws allow 128 bits encrypted files transmission.