Does adding any picture to your notes help? What about decorative images?

No — only images that carry the concept help. DECORATIVE, irrelevant images HURT, because they add cognitive load with no meaning.

Dual coding works when the visual encodes the idea: a labelled diagram, a process flow, a sketch that shows how parts relate. That visual does real explanatory work, so the extra processing pays off.

A pretty but irrelevant clip-art image does the opposite. Your limited working memory now has to process a picture that adds no understanding — extraneous cognitive load that competes with the material you're trying to learn. The test isn't "is there an image?" but "does this image teach the thing?"