I think you would have a tough time with simply EXIF metadata, but there are other options.

If you would expand your selection to include a histogram that can evaluate the complete tonal range of an image, you could get a rough idea if it was cloudy or not based on the contrast of the image. Contrast is typically not something that can be understood simply by looking at the standard EXIF data though, as the aperture, shutter speed, or program mode selected does not typically do much to indicate the contrast - although with some interpretation it could.

Take a look at this answer and specifically the section on contrast for more information: How and why do you use an image histogram?

Can you estimate whether or not the sky is clear from a photographs metadata?
Following answers on this website (like: How to use TeX Live on Fedora 17? and Manually installed TexLive on Fedora 16 )
I installed texlive manually on fedora and it works flawlessly.

The problem I have is that tex is a requisite for other packages (such as R). Whenever I try to install (through yum) R i am required to install another tex  from fedora.
 I don't want to do so because the package is old, it doesn't have tlmgr and I don't want to have two installed tex.

Is there a way to make the OS notice I already have tex installed and the dependency is satisfied? 
Thanks!
