Optimizing images for SEO is a controversial, overlooked and underutilized tactic.

The main argument against it is that it encourages image theft and hot-linking. That might be a small price to pay in comparison to the potential payoff, though.

However, keywords can lead to conversions. Consider phrases like “Wynn hotel room pictures”, “angry birds halloween costume”, or “navy blue one piece swimsuit”.

Users searching for such images are often researching those products, and may be planning to buy them. (Even for those who aren’t, you get the opportunity to imprint your brand upon them.) They will often bookmark your pages and comeback to them later and make a purchase.

In this article we will take a look at some the best tactics for accomplishing that goal.

Optimizing Image File Names: Use Keywords

From an organizational workflow perspective, it makes sense for most eCommerce retailers to name their images with a product number (or SKU), as this helps them to quickly match images to their respective products.

This is a wasted opportunity from an SEO perspective, as your product numbers or SKU’s have little relevance to anybody outside of your store. Customers search using natural language using search terms such as “small gold hoop earrings” and not “sku 345812345″”. You’re missing out.

A compromise would be to include both keyword terms and SKU’s in the naming of images files. You could do <gold-hoop-earrings-3432.jpg> or  <3432-gold-hoop-earrings.jpg>.

The first gets better priority on search engines (because of keyword prominence), but we recommend using the second – it makes life much easier for the people responsible for your site’s day-to-day maintenance. You save them time and effort, which can ultimately be put to better use on less mindless minutiae.

Next you’ll want eliminate stop words and low value keywords, and replace the spaces with a delimiter. The optimal word delimiter is a hyphen, Google and the other search engines have gotten better at working with different characters as delimiters, but there’s really no reason to be creative in this regard.

You don’t want too many keywords (which surely sets off “keyword stuffing” alarms). The fewer keywords you use the better. <12345-gold-hoop-earrings-small> is good. <12345-gold-silver-bronze-earrings-accessories-hoops-dangle>, not so good.

Search engines are pretty smart these days – if you put your image on a product page, it might just turn up when somebody searches “gold accessories”, even though it isn’t in the filename. So do everybody (and ultimately, yourself) a favour – keep it succinct.

Optimizing Image File Types
Use standard image file types such as “.jpg”, “.gif” and “.png”. Again, there’s nothing to be gained from being innovative in this area – unorthodox file extensions just look suspicious, to both users and engines.

You want to use the file type that gives you the best trade-off between image quality and file size. Experiment! Changing file types (especially for photographs) can sometimes drastically reduce file size without affecting quality too much.

Google and the other search engines can work with all three image types mentioned above, however in practice I have seen some preference given to “.jpg” and “.gif” over “.png” files.

Optimizing Image File Sizes

In recent years, search engines have begun to use file and page sizes as a secondary ranking factor. That means you’ll be punished for using oversized pictures. So it’s in your best interest to use images that have been sized to the size you are using on the page, and not resizing by using CSS or inline HTML.

Serving a 500px x 500px image and using CSS or inline code to resize it down to a 150px image is going to increase your page load time, especially on pages with multiple images like an eCommerce category page.

Make sure you save the image in a web-optimized format. Desktop image editing software often includes a preview or other “unnecessary” information which makes the file larger than it has to be.

A secondary part of image optimization concerns the pixel size. You want to make sure your images are a common size or have a common ratio of height to width. Square image sizes are the safest as search engines understand these the best. If you are going to go with rectangular sizes, your safest bet is to choose something with a 3:4 or 4:3 height to width ratio or a ratio that matches the golden ratio. if your image has height to width ratio which falls “too far” outside of one those common aspects you are working from a disadvantage.

EXCEPTION: Conventional desktop wallpaper sizes have immunity against this, because they’re common and widespread.

Optimizing Images with Magnification Software

Lately, many retailers have begun to use image magnification software, to allow customers to zoom in and see the items in detail while shopping.

This provides a great user experience, but it can works against your SEO. Most of the software uses flash or AJAX, which renders the image file invisible to search engines.

So you need to either do user agent agent detection and serve a straight image to the search engine spiders, or use a <noscript> tag. Serving content strictly based on user agent does fall under the technical definition of “bad cloaking”, so ideally using these two solutions in conjunction with each other would prevent you from looking like you are trying to “trick” the search engines.

Of course, this is ultimately a trade-off you must make. If your customers love being able to zoom in, then you should give them what they want. If they’re generally indifferent to it, though, then you might as well get rid of it.

Optimizing Images With Alt Tags

ALT Attribute Tag was originally created for visually impaired browsers or other screen readers to let the user know what the image they couldn’t see was showing. (Fun fact: Did you know that there’s alt text commentary on every xkcd comic?) Search engines do give some weight to the text contained in an ALT attribute. Be descriptive, but don’t stuff. (Follow the same guidelines for naming your image – 3 to 5 words is plenty.)

Optimizing Images with Heading Text & Surrounding Text

Placing the keywords that you want to rank for and that accurately describe the image in a Hx Heading Tag and in the surrounding text give the search engines more hints about what the image is actually a picture of. Be descriptive.

Optimizing Images for Conversions

If you are going to perform image optimization the most critical aspect is optimizing for keywords that are going to bring customers that will bring them into the conversion funnel. For example, optimizing an image for [Bellagio Hotel Room] is very likely to bring in a consumer who has high intent of booking a hotel room at the Bellagio Hotel if you can keep them on the information scent.

Takeaways from this article:

• Optimize your image file names with 3-5 words omitting stop words and using hyphens as a word delimiter
• Optimize your image file types with common images file format like “.jpg” and “.gif”
• Optimize image file size to make your images as small and fast loading as possible
• Optimize your image file size to be square, or well proportioned rectangles
• If you are using image magnification software, use alternate search engine friendly implementations like <noscript> to get your larger images indexed
• Optimize your images with descriptive alt tags, without overstuffing them full of commercial keywords
• Use heading and surrounding text to re-enforce keywords
• Choose image keywords that are likely to get browsers who have a good possibility of turning into customers

Image credit: BigStockPhoto/t.s.choong