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

Question

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 the 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?

Answer 1

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.