A picture is worth a thousand words, except when it comes to Google's assessment of your content. In this regard, you have to tell Google what the photograph is about because Google, as smart as it is, hasn't come up with a way to judge the quality of a photograph. What's left? A description in the alt or title tag and Google's assessment of other factors like how long someone stays on a page with an image. Qaulity images can generate enough interest for people to stay longer on a website, which is a Google ranking algorithm, but keeping someone on a website for the two minutes or so required by Google is a challenge for several good photos, let alone one. Of course, a slideshow may do the trick, but people tend to get through those pretty fast too. The answer is to also have interesting content that engages your reader.
Here's a photo of an iron fence.
While the photo may or may not be of visual quality or even interesting, the visit will last longer if you explain what the photo is about or something about how or why it was photographed this way. In this example, it was the lead-in photo about emphasizing light in photography I took a series of photos where I used a wide aperture, producing a shallow depth of field in high contrast lighting where the subject was well lit but the background was in shade creating the contrast "pop" associated with the best hours for photography- just after sunrise and just before sundown.
Nevertheless it is just one photo, so it's best to move on through several:
This is another example where some explanation is needed. This photo reminded me of CS Lewis' lamp post in Narnia- familiar to many who've read the book or seen the movie, "The Lion, The Witch and The Wardrobe" but fewer know its origins from centuries earlier via a time warp when Jadis used an iron bar from a London street lamp as a weapon at the creation of Narnia. It simply grew into a living lamp that became a landmark in Narnia.
What I have also done here is to use generously worded descriptions in the Alt tags of the photographs. That's like extra content for Google and, if relevant to the post, can get indexed in image searches as well as to verify the article content.
Will these two images keep a reader on this page for enough time to avoid a "bounce" being recorded by Google? Perhaps not, but an engaging video may just do the trick: