I can see the problem. Image has wrong information in its header. But what to do with it? As I mentioned before, I create context source by another script (PHP script) and php runs context. I have thousands of images so it is impossible to me every single image convert. But I created php gate which try convert images on the fly. When I try this particural image convert it gives me this image:
http://cdn-images-squared.tripomatic.com/e46c68903d2c4445f05a0369578c17dd-270.jpg
But after context runs this file it falls down with error message:

!LuaTeX error: reading JPEG image failed (no JPEG header found)
 ==> Fatal error occurred, no output PDF file produced!

mtx-context     | fatal error: return code: 70

Which is even worse, because although the user gets bad PDF it contains some information. In this case there is no pdf created. I looked in gimp for something bad in this image, but it looks ok to me.
So do you have any advice what to do?
Thanks

2012/11/26 Martin Schröder <martin@oneiros.de>
2012/11/26 luigi scarso <luigi.scarso@gmail.com>:
> It has 240x160 pixels and 1ppi, so it's 6,096 meters x 4,06400meters

I doubt that 1ppi is intended. :-)

Best
   Martin
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