Image Optimization: Overview
Unlike normal web pages, which are often rich with text content, image search is much more difficult for search engines to perform. The image itself provides few clues to the content within it. Although search engines are experimenting with techniques such as optical character recognition (OCR) to read text content within images, most images don’t have any text to read.
Search engines are also making use of facial recognition software to be able to determine when an image is of a face versus a body, or something else entirely.
However, although these types of technologies are very useful, they are limited in terms of what they can do. For that reason, success in image search optimization depends on using all the signals available to you to increase the search engines’ confidence in the content of an image.
This certainly includes the basic SEO techniques we have discussed in this book. The web page’s title tag, the H1 heading tag, the on-page content, and links to the page are all factors in image ranking. For example, if you have a single image on a page and it is a picture of the Golden Gate Bridge, and the title, heading tag, and page content all support that, the search engines'confidence in the content of the image increases. The same is true if you have 10 images on a page of many different bridges, and that is reinforced by the title, heading tag, and content. Consistency of content and theme is important in all of SEO, and it is especially critical in image SEO.
You should give particular emphasis to the text immediately preceding and following the image as well. This is what the user most closely associates with the image, and the search engine will view it the same way. A descriptive caption underneath the image is helpful.
Image Optimization: The Ten Most Important Things To Further Optimize Your Images
Image Optimization: The Ten Most Important Things No.1
Make sure the image filename or IMG SRC string contains your primary keyword. If it is a picture about eBay Store SEO Tutorials and Courses, name the file ebay-store-seo-tutorials-and-courses.jpg and/or have the SRC URL string contain it, as in http://seouniv.com/p/ebay-store-seo.html.
Image Optimization: The Ten Most Important Things No.2
Always use the image alt attribute. The alt attribute helps the vision-impaired to understand your site, and search engines use it to better understand what your images are about. Recent research by the authors indicates that this feature is still not used for lots of sites' images, and that many sites have tried to use it with invalid HTML. Make sure the alt parameter is valid.
Use the quotes if you have spaces in the text string of the alt content! Sites that have invalid IMG tags frequently drop a few words without quotes into the IMG tag when they were intended for the alt content; with no quotes, all terms after the first word would be lost, if any would be used at all.
Image Optimization: The Ten Most Important Things No.3
Avoid query strings for IMG SRCs just as you should for page URLs. Or, if you must use URLs that include query strings, use only two or three parameters. Consider rewriting the query strings in the URLs so that they do not contain an excessive number of parameters, which will cause spiders to refuse to crawl the link. Note that Google claims to no longer have problems with these types of situations, but it is better to be safe than sorry, and other search engines have been less clear as to whether this is still an issue for them.
Image Optimization: The Ten Most Important Things No.4
Use good-quality pictures, which will read well when shown in thumbnail format. Good contrast is typically the key here. Lower-contrast images are visually harder to read, and it is common sense that if the thumbnail image doesn't look good, it will not invite a click.
Image Optimization: The Ten Most Important Things No.5
Do not save images as graphics files with embedded thumbnails—turn this feature off in GIMP, Photoshop and other image editing software. Search engines may copy your image, reduce it in size, save it in compressed format, and deliver up a thumbnail of it for their results pages. An embedded thumbnail can wreak havoc with some compression software, and it increases your file size slightly, so just leave that feature turned off.
Image Optimization: The Ten Most Important Things No.6
Don’t store the image in a sidebar column with your ads or inside the header/footer navigation elements; otherwise, the engine algorithms will ignore the image as irrelevant, just as they ignore page decor and navigation graphics.
Image Optimization: The Ten Most Important Things No.7
Have a proper copyright license! You need to have a proper license to display the images found on your site so that you don’t get sued. Be careful about trying to use images from Wikimedia Commons or other public stock photo sites since you cannot be sure that those images really are in the public domain.
Image Optimization: The Ten Most Important Things No.8
If you are using images that may also be displayed on other websites, store/display them at different sizes from how they were provided to you. Don't change only their HTML IMG tag height/width parameters; reduce the size of the images or increase or decrease their compression and then resave them so that they have different file sizes.
Consider adding a watermark with your site URL to the image. This can bring traffic to your site, and it also discourages people from stealing your images.
Also, try altering the aspect ratio of the images a little bit—that is, make sure the height-to-width ratio of the images is different from images on other sites. You can do this by slicing a few pixels off the height or width of the graphic and resaving it. You need to change the file sizes and aspect ratios only if you are redisplaying image files that may also be found on other websites. This is particularly the case for licensed content, such as movie graphics, news article graphics, affiliated content, and manufacturer product images.
By changing the image files somewhat, you will help to ensure that the search engines perceive your content as being sufficiently original, instead of throwing it out of the SERPs after hitting a duplicate content filter.
Image Optimization: The Ten Most Important Things No.9
You need to ensure that your server configuration allows your site’s images to be displayed when called from web pages on other domains. Some system administrators have disabled this to keep people from displaying their images on other sites, and this could cause problems if you want your images displayed in search engine image search results pages. Likewise, make sure that your robots.txt file does not block the crawlers from accessing your image file directories.
Image Optimization: The Ten Most Important Things No.10
If it is a fit for your business, specify that others are free to use your images for online display as long as they link back to your website from a credit line below the image or adjacent to the image where they display your copyright notice. Enabling others to use your photos invites more promotional attention when people wish to write about you in blogs or in news articles.