Force Preview to Open an Image File
Recently Preview.app was refusing to open some image files for what seemed like no reason, I wasn’t even able to drag the image file onto the Preview icon to open it. I know the images are fine because they open fine in Windows and even in Photoshop, so how can I force Preview to open the images? Pretty easy really: hold down Command+Option keys while dragging a file onto the Preview icon, this will force any file to open through Preview (you could force a text file into preview if you wanted with this, but obviously preview will only render compatible files).
Using this method, the images worked fine, I was able to resave them, and now they’re back to opening in Preview as usual. I’m not sure what the cause of this problem is, perhaps the image EXIF or meta data was corrupted. I remembered this trick from a post a few years back by our very own David Mendez, how to force open a file in Mac OS X, and this actually will work with nearly every application and file, so if you want to force an image file into TextWrangler, you could do that too.

[...] iPad templates. If you’re having difficulties or want to try on an older version of OS X, try forcing Preview to open the file by holding down the command+option keys while dragging the .key document onto the Preview apps icon [...]