The alt text is what gets used for those people who can’t see the image. Unless the image is being used for a different purpose in each page it ought to have the same alt text as that is what people who can’t see the image will see or hear instead.
The only time that an image should have different alt text on different pages is where the purpose of the image is different. For example if you have a photo of you and your dog and one page is about you then the alt text might say ‘me with my dog’ while the same picture on the page about your dog might simply say ‘my dog Fido’.
Whatever alt text you use should convey the same meaning as the image would.
I cannot conceive of a situation where the same image would identify which page you are on for more than one page. If the image is supposed to identify the page then a different image would be needed for each page.
<img src="path-to-my-static-image" width="379" height="70" alt="<?php echo $_SERVER['SERVER_NAME'];?>" />
And replace SERVER_NAME with a parameter from the following list:
<?php print r( $_SERVER ); ?>
The alternative text has nothing to do with SEO. The intention of that attribute is to tell those people who can’t see the image why the image is included in the page. The text MUST relate to that reason or it will be meaningless and blind people and those with images turned off will be uable to use your page properly.
Try reworking the text that everyone can see if you need to update the page for SEO purposes.
Yes but the Google search engine bot effectively is a blind person as it can’t see the image. Of course for every bot that can’t see the image there are THOUSANDS of living people who can’t and the bots are trying to treat the page the same as those people do so targetting the real people is the best thing you can do for SEO.