You can add fade weight by entering the image's edit mode. First, hover over the image and click the pencil icon. Then, you can add a fade effect by clicking the fade effect tab. Finally, type in the fade weight percentage in the box or adjust the slider to the left or right.
Fade weight is the amount of fade of the image from 0-100%.
You can either increase the fade weight making the image appear more blurred or decrease the fade weight making the image less blurred.