Which ways are there to give images a blur effect?

Question

I'm a little bit stuck here..

This is the page I'm working on:

The issue I'm having is that the images in the 'In der Nähe'-box on the right seam to have a blur effect on them. And I can't figure out where that is coming from.

I suspect CSS, or JS since when opening the images in a new tab, they show as bright as they are:

Usually Firebug, or Chrome Dev Tools help me finding the origin of such issues, but in this case I can't find any opacity or filter attribute in there.

What am I missing? What other ways are there to give a blur effect to an image?

Answer 1

There's an opacity: 0.7 rule on the entire div; the one of class notes.

Answer 2

As Lightness Races in Orbit (what a mouthful!) points out, there an opacity: 0.7 on the class .notes BUT that is not everything. All those images are upscaled. I.e. there actual size is smaller than the rendered size. This may cause the image to be less sharp than it should.