In this case I can recommend dictionaries like ABBYY Lingvo that support text-on-image recognition. They are not free, of course. It works like this: you point to a word with the mouse and press left Ctrl, then Lingvo recognizes the word and shows its vocabulary card in a popup.
As for me, I never look up unknown words in dictionaries when reading parallel texts, that could just ruin all the fun for me. I go on reading and slowly but steadily get to understand and remember the meanings of those words — magically!![]()