One of friend told me about changing the properties of the image - gif or jpg or pdf or word files may affect the search engine ranking. Will it work? As per my experience the crawler can read only the final output from the page, so is it worth to change the properties of these files or chaning the name of the file is enough?
Manish, search engines can certainly crawl word and pdf files. I have several with Google PR6. The engines also read the alt text of gif and jpeg files. However, if you change a file from .html to .pdf etc it changes the url.
Changing properties (say filename) of jpg or gif files might change ranking on image search but not on your page that contains them. They are certainly not visible to Googlebot but only to Google Image Bot. For PDF and html, as mentioned, it will be treated as new page once you change its filename so I doubt if it helps.
Sure about that? Our reseach suggests that image filename and alt text can have a marginal influence on Google SERPs. Not enough to really bother with unless you're in a highly competitive market, and I believe it's easy to get carried away and trigger a spam penalty, but I don't think that Googlebot 'Ignores' alt text
Image filenames and Alt texts do have an influence on the pages position in the SERPs. Not a big influence though.