Modern cameras can store raw images which are a must for a serious photographer. Unfortunately raw image previews are not shown by Gnome's file manager Nautilus.
However, there is already a workaround type of solution for this. I will describe it in four steps.
Step 1:
Install gnome-raw-thumbnailer package.
Step 2:
Create a file /usr/share/thumbnailers/raw.thumbnailer
Step 3:
Put in these lines:
Exec=/usr/bin/gnome-raw-thumbnailer -s %s %u %o
MimeType=image/x-3fr;image/x-adobe-dng;image/x-arw;image/x-bay;image/x-canon-cr2;image/x-canon-crw;image/x-cap;image/x-cr2;image/x-crw;image/x-dcr;image/x-dcraw;image/x-dcs;image/x-dng;image/x-drf;image/x-eip;image/x-erf;image/x-fff;image/x-fuji-raf;image/x-iiq;image/x-k25;image/x-kdc;image/x-mef;image/x-minolta-mrw;image/x-mos;image/x-mrw;image/x-nef;image/x-nikon-nef;image/x-nrw;image/x-olympus-orf;image/x-orf;image/x-panasonic-raw;image/x-pef;image/x-pentax-pef;image/x-ptx;image/x-pxn;image/x-r3d;image/x-raf;image/x-raw;image/x-rw2;image/x-rwl;image/x-rwz;image/x-sigma-x3f;image/x-sony-arw;image/x-sony-sr2;image/x-sony-srf;image/x-sr2;image/x-srf;image/x-x3f;
(Steps 1, 2 and 3:)
http://ubuntuguide.net/raw-cr2-image-pr ... -thumbnail
Step 4:
Nautilus/Settings/Preview
Set Max Size to something more suitable than it is now by default. For example, there are options for 1, 5, 10 and 100Mb. My camera's raw images are 15 Mb so I have to choose 100Mb.
This worked with 64-bit Mint 12.