I am running a photography website for my girlfriend, and currently trying to improve the site's loading speed. It is a photography website, and thus many images are loaded, which makes it a little slow. This is expected and accepted to some extent.
However, when I looked at the waterfall diagram in Chrome, which shows loading time of different resources, I noticed that "DNS Lookup" of some images takes up to 6 seconds. This is weird, as the images are hosted on my own page, and other content (css, html) has already been loaded from the same domain at that point, so no additional DNS lookup should be necessary. What is happening here? Is it really a DNS lookup? If so, why does it take so long?