<IfModule pagespeed_module>
ModPagespeedRewriteLevel PassThrough
ModPagespeedEnableFilters remove_comments
ModPagespeedEnableFilters collapse_whitespace
</IfModule>
-pagespeed-dev
+mod-pagespeed-discuss
Your understanding is correct. With that config PageSpeed should only
be removing comments and whitespace.
If you look at the html source of your page with PageSpeed on and look
for the tags for these images, what do they look like? Could you
paste them here, or share a link to your site?
<input type="image" src="image.gif.pagespeed.ic.skb55JoPUg.png"..