Why is it bad to just have one big picture as your homepage?

When designing my homepage, I feel like the common knowledge is that it is bad to just have one big picture in the center that gives all of t开发者_如何学JAVAhe content. The "right" way to do it would be to chop up the large layed out image into several small backgrounds and make the text use standard html with css background images for layout.

Is the only reason one big image is bad SEO reasons?

1. A search engine can't make sense of it.
2. A blind or otherwise visually-impaired person can't make sense of it.
3. Someone blocking images because he's on a mobile phone with expensive internet can't make sense of it.

There are a few reasons :-)

Also important:

1. Changes are not easily made to whole, pre-composited images, unless you still have access to the original layered variants. And hopefully they contain text as well, not just pixel data. (Mentioned by others before already. Credits go to pierre and Kendrick)
2. If you're using background images don't forget to set a text and background color too. Otherwise people not seeing any images might have a hard time deciphering your text (black on black isn't nice to read :-))

You can still use one large image as background. How the text is layed out above that is another matter entirely. In fact, chopping up the image and piecing the pieces together is painful using CSS too. In my experience it's best and easiest to leave background images unchopped and instead composite the rest of the layout above them, using other images or backgrounds if needed. This gives you a little more flexibility when changing a layout again, too.

SEO is one. Handicapped accessibility is another big one -- a screen reader can't read text within an image, typically. Page load time is another one; a user with a slow connection won't see anything useful while the image loads. Lastly, many browsers will use multiple connections to request resources such as images, so they can be loaded simultaneously. If there's just one image, only one connection can be used.

Updating will be tedious; you can also no longer rely on many benefits of CSS.

It's also bad for accessibility (screen readers, text-resizing, different monitor sizes)

It also removes your ability to easily edit text content.

I certainly wouldn't do it if you're looking for a web-developer job, but if you really don't care about the above, you won't be the first person to do it...

I see no reason at all in using imagea to represent something what can easily be achieved with HTML and CSS.

You're putting up a web site to enable communication between you and your visitors. Images and Flash prevent that.

Generally, you design a site with HTML/CSS and text. Only when you wish to add some design that cannot be expressed with standard means, then you use images. But have your site degrade gracefully for those who cannot or does not wish to see images. Let images be an addition, like an advanced version, in no case a replacement for text.