LockImage is a free open source software to protect your images with a password. LockImage protects an image by converting it into a password protected executable with an embedded viewer. It consists of exactly one file and does not need any installation. All you need to do is to download the software and run the exe file. From the file menu of the software, select Open and open any image you want to protect.
Now select Save As and you will be prompted to enter the password for the file. Once you click ok, an exe file will be created with the name provided. Whenever you open the exe file for viewing the image, it will again prompt for the password. Once you enter the correct password, the image can be viewed with LockImage.
This is a great utility to protect images, especially if you are sharing them over the web. The only problem with this utility is that the image becomes and exe file and e-mailing this could be a problem as most of the e-mail services do no allow .exe files. But then there is always the zip utility to send files.