How i can popup an image that display for 5 second as slogan/announcement after opening my sharepoint site welcome page
As Example: http://www.lebanese-forces.com
You need to make a custom webpart at the least maybe a template. If you are already using a custom template on your site that may be easier.
In your web part you need to do something akin to the following (I have chosen this code to be a lightweight solution which will require minimal code and very little browser/device power)
If you are using SharePoint 2013 you can add this in the head, but if you don't care about validation (You're using 2010 it can go in the body :P)
This all gives a nice lightweight solution, that is cross browser and looks really sexy.