ImageGear provides a pair of image processing functions that perform image encryption/decryption operations. These functions change the image bitmap,  modifying the format of the pixel data stored within it.

IG_IP_encrypt()	Encrypts the image bitmap using the specified password string. To successfully decrypt the image bitmap, the specified password will be needed.
IG_IP_decrypt()	Decrypts an image bitmap using the password string specified during encryption. If the password is the same as used with IG_IP_encrypt(), then the decryption will be successful, and the original image bitmap will be restored.