How to optimize images?
The listing of images on the Google search engine depends on many factors.
The content of the alt attribute applied to the image. Please note that this attribute is supposed to contain a description of the image for users unable to display it. It is not supposed to contain a series of keywords.
The text content near the image. Google is apparently trying to identify a new caption.
The name of the image file. Note than this parameter seems to be useless for the visibility of the page displaying the image on the conventional search engine.
The originality of the image. Being the only one to share the file is preferable.
The popularity of the page and its ranking on the given keyword.
The popularity of the image in terms of links.
In a monetization logic, the traffic coming from image search engines convers much less commonly.
The number of searches made on this type of engine is indeed much lower than those made on generalist search engines. The volume of traffic we potentially can get is therefore often low.
Sometimes, images rank on Google.com (the universal search mechanism). In this case, the traffic generated can become much more interesting if the image meets the internaut needs.