I find that my students often have a superficial understanding of aspects of how computers work that persists even after they've been explained. For example, after giving instructions to 7th graders recently to save cropped screenshots they were taking as jpegs to upload to voicethread, I saw one student navigate to her psd file in Windows Explorer and simply change the file extension from psd to jpeg. No, that won't work! I've been doing a lot of research lately about the need to provide visual representations of concepts, especially for girls, who tend to process information in the language areas of the brain rather than the spatial areas. I left it free of text so people can make their own points with the visuals. The main points are layered information vs. compressed "flat" information, Photoshop-specific platform vs. universal program platform, and large vs. small file size.
Photoshop vs Compressed Image from Erik Nauman on Vimeo.