The answer sorta depends on one's point of view and how detailed one wants to get when it comes to going after every bit of traffic. Hosting the images elsewhere eliminates any hope of receiving traffic from image searches, and misses opportunities to have a few extra keywords in URI's the engines may take into account.

But, for the most part, it should not matter much. Lots of sites these days pull images from secondary locations. I suppose it is also possible that images hosted off-site is some sort of red flag indicator (i.e., may have X% probability of spam associated with the practice), but that only means that you need to keep the site clean when it comes to SEO practices. And that is something you should do anyway.

it might even help if it also improves page load time.

Also, note that many of your readers that read your blog from their workplace will not be able to see your pics if they are hosted on an external site, since most shared-media website are blocked by network administrator.