When we capture a photo we get an image. No matter whether it is a Nikon or Canon camera or other Digital Single Lens Reflex (DSLR) or even a very normal digital box camera, all of them are capable to capture a digital image. But in this article we will have a look about a digital photograph on behalf of a search engine. We think about an image file name which is very much search engine friendly.
So, what is a search engine friendly name? When we took a photo the name of the digital file/raw file like 32017007.JPG. Is it very much friendly for anyone to remember? May be you took a photo at Sydney Harbour Bridge last december. The file name was SAM34562345.JPG and after that, last two months you took hundred of even thousands of photo. It's very natural for you to forget the name of that particular image. Search engines are not any exception. Search engines like Google of Bing also likes a name of an image which is easy to read. If we rename the image Sydney-harbour-bridge.jpg it is better understandable for google or bing. They can realize it easily that this is an image of Sydney harbour bridge. Naming it SAM34562345.JPG is meaningless and not descriptive at all. Which is very hard not only for humans but also for the search engine robots.
Google or bing does not understand the content of an image. When they reach at any image they just read the image file name, it's metadata (i,e file name, size, pixels, location sometimes). Search engines doesn't understand the content of an image. They don't know whether it is an image of a bird, a dog or images of other planets by NASA. They just understand the file name, the metadata(which we need not think about much), the ALT tag, and if we have any description about the image.
Now we can move forward. Some time we rename an image "Sydney Harbour Bridge.jpg" to "Sydney-harbour-bridge" or "Sydney_harbour_bridge.jpg". What is the difference among the three? We can use space between words, or we can put a hyphen(-) or we can use ( _ ) underscores. Which one is the best method? This is quite a technical question. spaces can misguide everyone, may be we can put more than one space by mistake, so, avoiding spaces is better.
When we rename a file with underscores ( _ ) any intelligent system like google thinks it is a single word. The three word "Sydney_harbour_bridge" search engines will think it as a single word like "Sydneyharbourbridge" which is quite difficult for search engines as well as humans. So it is always better when naming a file always use hyphens (-) between words. When we use hyphens(-) google search engines and web servers like Apache/IIS (sorry, this is a technical term, but not very difficult one) treat it every single word between hyphens(-).
Ok, lets clarify it again. If we write A-quick-brown-fox-jumps-over-a-lazy-dog, search engines and web servers will think it has nine individual words. But if we put underscores( _ ) like A_quick_brown_fox_jumps_over_a_lazy_dog search engines won't understand it as seperate characters. They will think it is a single word. It's hard for them to recognize.
What is our aim at the point of image optimization? Our aim should be indexing our image file to google uncle easily and rapidly. So one way to optimize image file is using a descriptive file name and using hyphens between words. Try this techniques while upload your next photo in facebook, twitter, instagram or even other professional image sites. If you want to learn more about image optimization read Importance of Image Optimization.