Header image not showing

Hello All,

I’m in need of some really urgent help.
I’m designing a website on WordPress using the twenty twelve theme. Each time I upload the a header image using the Appearance > Header, then upload the header image. But when I do that it appears on the browser I used to upload it on. But not on any other browser or computer. If i delete cookies cache and history on the browser I used the header image won’t appear although in the darshboard it shows that it’s uploaded.

Please urgently needing help.

the website is https://www.surreys-neatfreaks.com