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Earlier this year, I had the fantastic pleasure of attending CSSConf EU. Among the great talks, Una's particularly stood out.
Along with the talk, Una published a series of blog posts going over the building of various CSS image effects using blend modes and other clever tricks. These are accompanied by some very interesting Pens, which are definitely worth checking out!
To go one step further (because why stop there!), Una has also made a library in Sass and CSS, called CSSgram which allows you to show your images with Instagram-like filters, solely through the use of CSS.