I would like to reproduce these object conforming brushed strokes to highlight. I saw these at:
These highlights also include a single right cancel and left cancel, and could be placed and fit/conform around/on on any size object.
p.s. I have now communicated with the author, and was kind to explain that the slides were created in Apple's Keynote software, though a similar effect could be achieved via PowerPoint. Specifically, the equations were typeset in the application called LaTeXiT, and copy/paste them into Keynote. The crosses and circles are then drawn using built-in shapes in Keynote.
It may be possible get a similar effect in LaTeX/Beamer without too much effort? One route is to use TikZ to get the brush stroke effect? Another is to use the `overpic' package to take an external image of the brush strokes and place them over the text. Here likely need to use a PNG file, so that part of the image can be made transparent.