Images are exported into the "images" folder, if they are placed in Muse or used as a fill. They are in the "assets" folder, if they are linked for download or if they are used by 3rd party widgets.
Try to use "%20" instead of "_" or "%". Or better: Rename all images, which are using a blank in its file name re-link them and re-publish the site. You can easily identify these images by exporting your site as HTML.
don't use "." in the name, thats basic html
p.s, here is one of mine ... the ?crc=1228116220 at the end indercates the image is resized
so the pure image =