A modern site cannot exist without graphic elements that make the design attractive. You should, however, use images carefully and think through the page design that uses graphics.
First of all, you should always fill the ALT attribute of the <IMG> tag. Any image on the page can have “alternative text” specified in the ALT attribute of the <IMG> tag. This attribute is useful for two reasons:
If, for some reason, the image embedded into a web page is unavailable, the text provided in the ALT attribute will be displayed instead to give the user some idea of the content.
Information from this attribute helps the image robot that indexes pictures for Yandex.Images. If the ALT attribute is specified, it makes easier for the search engine to understand what this picture is.
Second, you must duplicate the text represented on the image. Yandex robot, at present, cannot recognize text represented as image, and the text from the ALT attribute does not get into the main index. For that reason, you should not use pictures as replacement for text. If using a graphic element that contains text is absolutely necessary, duplicate whatever is written on the image as text. Then no information required for correct ranking will be lost.
Specific details of using graphic images:
Graphic menus. Site menus that consist of pictures (instead of texts) enables the user to navigate to the internal pages but does not tell Yandex what information resides on these pages. You should provide, whenever possible, an alternative text-based menu with links to the main site sections.
If the site is designed using flash technology, create an alternative text-based version. It will be useful to the users who do not have Flash installed or who have an out-of date version of Flash, and the users who accesses your site from mobile devices, as well as to Yandex robot, enabling it to index your site completely and without errors. There are some limitations upon flash indexing (see the “Site indexing” section).
Some more advice on improving ranking on image search:
If the images illustrate some text, place them as close as possible to the appropriate part of the text. If this is impossible for some reason, accompany images with captions located in close proximity to the images.
It is better to make image file names informative (e.g. not img_123456.jpg but ktulhu.jpg) and relevant to the image content.
If a text contains a link to a picture, the text of this link must also be informative (i.e. not <a href="paris.jpg">img. 1</a> but <a href="ktulhu.jpg">Paris at night;/a>).
Using robots.txt file, disallow indexing of CAPTCHA images and other automatically generated images (banners, charts, counters, graphic informers etc.)