As I understand, the folders contain the individual files in whatever format was used when saved (jpg, bmp, tiff etc.)
Your computer will give you the sort of listing you want. Thumbnails are just a way of interpreting the same file, but using this takes longer and more screen space to display a lot at once.
When using My Computer the operater can choose (in View), how to see the filed pictures.
Look at "View" and choose from "Thumbnails" to "Details" as well as four others.