Working with background and header images

Hello,

I am creating a simple webpage and applied a background image to its Master Page.

I added a 3X3 HTML table and applied to top cells some images which are presented above the background image.

Every time that I click on menu and generates a postback these images flicks, giving the idea that they are always downloaded and refreshed every time that is generated a postback.

Once I am using a content placeholder to hold the web pages, these images never change, so I want download them just at 1^st time that I load this web page reducing the quantity of information on subsequent postbacks. Besides turning the page lighter, its presentation is more pleasant, once the image stops flicking.

My questions are:

I am doing this well?

If so, there is a away to define that these images are ever the same and stop the flicking?

I am not sure, but maybe I am wrong on that part where I say that reduce the quantity of information on subsequent postbacks, because at first time the page is runned on client browser the images are downloaded to local folder "Internet Temporary Folder" and used later. Is this true?

Thank you and Best Regards,

Jo?o Ferreirinha

How the browser manages images is beyond your control. Images may be cached anywhere between your webserver and the browser, or nowhere, in which case they will be downloaded each time. My ISP may cache images, for example, or they might not. I might go through a proxy server elsewhere, or might not. I might decide not to keep anything in my temp folders, or I might set it to retain 2GB of data. As a web developer, these things are out of your control.
They are probably just being rerendered, not actually downloaded again. IE and FireFox both cache unchanged images. If you want to be certain of that install Fiddler and watch the request. I have a couple of sites with background images and the like. Whether they flicker seems to depend on a lot of different factors. Even if they aren't downloaded the browser may send a request to the server to see if the resource has changed. If the server takes a few extra milliseconds to respond to that then you might see more flicker on that request. Other things might also make it more likely that you'll see flicker. Do the images have transparency? Are you setting a background color and then drawing the image over it?

Thank you for the answer.

The images are simple Jpegs, don't have transparency and background color.

Regards