Item page displays blank icons and corrupted PDF icon

Is there a way to get Omeka to display an appropriate file icon for files in an item so users know what they can choose from?

When I create and item I'm uploading three files: pdf, epub and odt. The icons show up but they are not labeled in any way except on mouseover when the filename pops up. The icons for epub and odt are blank generic "folded corner page"-like icons and the pdf shows an image that looks like an old TV screen full of snow. Different snow for every pdf, but snow just the same. In Minnesota, we are used to snow but it would be great to have icons.

I've seen other posts in the forums but no solution. Anyone have any ideas?

The pdf icon creation just started working correctly on my latest upload. Don't know why.

Otherwise the icons for the non-pdf files are blank and identical so the only way you know what they are is to hover over one.