Hi,
i use simple image gallery plugin here

bollywoodbook.in/posters/neha-dhupia-dons-the-coverpage-of-femina-india-magazine-december-2014-edition

there seems a right tick icon on the left side of every image which makes it look wierd
how to remove it

Hi. It's your template that is adding this mark to all li elements of your site. Try the following CSS code:

this doesn't works for me

li.sigFreeThumb { background: none !important;}

now if u check bollywoodbook.in/posters/salman-khan-shines-on-the-coverpage-of-forbes-india-magazine-2014-december-issue

when the cursor is taken to image there's tool tip - click to enlarge image salmankhan forbes.jpg and you are viewing the image with filename salmankhan forbes.jpg

salmankhan forbes.jpg must be removed and you are viewing the image with filename , the file extension .jpg must be removed

how to achieve this, plz help

Your template is using a lot of !important which is bad practise and overrides all other styles.
You can either remove these important attributes or use this snippet

As for the title, you can change the link's the ( <a> tag) title attribute and remove the filename.

Info on overriding this extension can be found here: www.joomlaworks.net/support/docs/simple-image-gallery (MVC TEMPLATING: THE POWER TO CUSTOMIZE YOUR GALLERY LAYOUT)