First rule about media on website: What you can see, You can download...
If you want to disable context menu's for images, you don't need jQuery.
It can be done easily using <img oncontextmenu="return false;" src="" />
Example: http://jsfiddle.net/GpJbU/
If you realy want to use jQuery you could use:
$('img').on('contextmenu', function(e) {
return false;
});
$('img').on('mousedown', function(e){
if( e.button == 2 ) {
return false;
}
});
Example: http://jsfiddle.net/sPdn6/
Edit
Using the base64 including preventing a context menu you could look at this example: http://jsfiddle.net/WfFxb But if you hit F12 (Developers tool) and check the "Network" tab you can still download this image. Thought, it is hard for a novice.