I have just downloads pictures from a Site, some shows displays and some not, the format of the pictures are same and that is JPG, I have tried some tips provided here on the forum but no result. The main reason I have found is that because of Dimension. When I open those images which have no preview has also no showing their dimensions. So it can be a problem that can helps for preview. If any experts have idea for this will helps me and all of the guys for the same problem.