Search engines cannot read images and figure out what picture it is. So, when you search for images, search engines depend on few other parameters to decide which image to be displayed in the search results.
Factors that affect the image search:
1. The content around the image where the image is displayed. For example, if you have the image of a "coffee cup" in an article about coffee, then that image may get listed in the image search results for "coffee".
If you have an image of the same coffee cup in a crockery shopping related article, that image may get listed in the search for "crockery shopping".
So the content of the page in which the image is used affects the image search results.
2. The name of the image file. When you upload the image of a coffee cup but you name the file as "Apple Juice", it will not be helpful. Your chances of showing that image in search results are low if you don't use proper and relevant name for the image.
3. ALT text used in the HTML tag to display the image.
You need to use the following HTML tag to display the image in a webpage:
<IMG SRC='CoffeeCup.jpg' ALT='Coffee cup' >
The "ALT" attribute represents the alternative text that will be displayed if the browser cannot display the image. In normal cases, this ALT text is hidden to the readers. However, search engines give some value to this ALT text and it can influence the image search results.
Use relevant keywords in the ALT text of the images. Do not leave any images in your web pages without a proper ALT text.
4. Position of the images within the content. Always place the images near the headings and keywords that are highlighted. The proximity of images to the keywords tell Search engines that these images are related to those keywords.
5. Post your images in to photo sharing sites and picture sharing sites. If they allow a link to your original article, use that and provide a link.
6. Add a watermark with your site name in the images so that even if somebody steal your image and use in other sites, you can get some publicity by having your site name on the image itself.
SEO tips for images
Here are some tips for optimizing your images for better SEO.
Use keywords for image file names. Replace the file names like IMG_1.jpg to meaningful names and include keywords in the file names.
Avoid SPACE and special characters in image file names. Use only alphameric letters and underscore.
Always use "ALT" attribute with your image.
Keep the ALT attribute value short and meaningful. Use a keyword ifpossible, but do not make it more than 2-3 words.
Always use TITLE attribute with image tags. Use keywords in the TITLE attribute of image. It can help in better search engine ranking. Also, title attribute is used as tooltip text by many browsers, so it will be helpful for users.
If you include text data in the images, reproduce the same data as text because search engines cannot read text data from images. Also, by presenting it in the text format, your users can copy the text and use.
Use good quality images. Some search engines like better quality images.
Use low size images. Big images will make your webpages slower to load and search engines hate slow page loading.
Place your images within the content and as close as possible to the relevant and related content.
Write your site name in the images so that you will get some publicity if your images are copied and used by someone else.
Importance of images in Articles
Images are very useful for your readers to better understand your content. Seeing an image can be more helpful than reading lot of text.
Search engines cannot understand the image and figure out what image it is.
You can add images to your article to give more value to your readers. But from search engine point of view, the images are not much useful.
So, to make the search engines and human readers happy at the same time, you may add some images along with a lot of descriptive text. Search engines love descriptive text and have no objection in using lot of images even though it cannot read the images.
Images are not completely ignored by search engines. It has some use like traffic from Image search but not as good as the value of good descriptive text.
Images can bring traffic from Image Search
Google and some other search engines have an Image Search feature where you can look for images related to specific topics and find images.
By using relevant images in your articles, you may get traffic from Image Search. When your images are displayed in Image Search results, people may visit your article page, thus helping you get better traffic through your images.
Avoid too many images
Avoid too many images in your articles. Images are heavy and will take a lot of time to load. In terms of the number of bytes the computer has to download, a small image is much heavier than the entire text in a big article.
A large article may be just 1 KB of data, but even a small image will be about 50KB or more. Large images can be about 1000 times bigger than the text of the article.
Plain text is easy to load in a browser. Images take lot of time.
When people have slow internet connection, page may not load if there are many images.
Search engine spiders may ignore the page if it cannot download the page within the time it expects.
In most cases, 1 or 2 images are ideal. You should use more than 2 images only if it is absolutely necessary.