How to optimize on google images?

I want to rank better in google images

All I know about google images optimization is:

1. Use alt tags with the keyword
2. Use text around the image with the same keyword
3. Image file name (thanks vagrant)
4. Websites with large number of images rank better (thanks diggits)
5. Keyword rich caption and title tags.
6. Dashes "-" are preferred more then underscores "_" (thanks MR. Gill)
7. .gif .jpg .png formats are preferred (thanks Jalpari)


Do you have other ideas?

 

keywords in the image file name as well rather than 147b.gif

 

I've added that to the list thanks

 

You said it all..

Ive also noticed that websites with large number of images / pictures are ranking much better on G images..

Must be some relevancy factor.

So, image will probably rank better if comes from some gallery of images which are closely related to search term.

 

Added that as well. Maybe this will be a useful thread for newbies.

 

Please use "_" for the image title or tag for more than 2 words.

 

How about Caption and title tags.
And Dashes "-" are preferred more then underscores "_"

 

.gif and then .jpg format is good