I'm not sure why it's including this in the export, but this is one of the default "Image Fills".

http://f.cl.ly/items/1X0M2o0V0f3A463c0a2H/Untitled_numbers.p...

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Pages does it too. Export a document in DOCX format and you get the same PNG file. Export a document in Word 97-2003 format and you get three of these PNG files!

http://mcmillan.cx/blog/2014/05/31/bloated-exports-from-page...

From the looks of the OOXML format, the image there is just used as a resource. http://web.mit.edu/~stevenj/www/ECMA-376-new-merged.pdf xl/theme/_rels/theme1.xml.rels refers to image1.png. I'd say it's a default background of some description. Still, it would be cool if there was something in there. Maybe taking a look at the frequency of the bytes would help?

Someone should run that image through a steganalysis tool.

It doesn't seem to be explicitly associated with Numbers, but with Excel: http://www.it-volpers.net/2011/03/21/disassemble-xlsx/

It doesn't happen to me. No strange image gets included when saving the spreadsheet.

Here's something interesting. The image only has 47 unique RGB values in it. 47 is such an arbitrary amount though. It doesn't go into power of two cleanly.

Can't be just a placeholder. If it was, it would be a single color for a better compression. Hence the whitenoise - it helps to maintain compression ratio low.

What is that image?Any answers from anyone in HN?

The first comment on the question itself makes the most sense to me.

Edit: Sure, downvote me ;)