To make an image transparent in varying degrees, use the property opacity and filter property to work together in all browsers.
The lower value of opacity more transparent the image.
The property "opacity" takes values from "0.0" to "1.0".
The property "opacity" in "filter: alpha" takes values from 0 to 100.
This can be useful to set an image as the background faded, you create a page background, but do not bother to read the text on the page.
To put a very blurred image, put a small value for "opacity".
If we go back to normal to leave the image, that is, to remove the transparency, we put the maximum to both properties "opacity".