I'm not sure if I've posted about this before but QuickTime Player 7 (Pro) has a bit of an odd bug in Snow Leopard and later with Preview.
1. Open up a movie and hit Command + E for Export.
2. Under the Export pull-down select "Movie to Picture".
3. Hit the Options button and select any standard image file format, like PNG or TIFF.
4. Notice that the name of the file ends with .pct no matter what.
5. Export the still image.
6. In the Finder, Get Info (Command + I) on the image. Notice it's a "QuickDraw picture"
7. Try opening it with Preview and behold this:
So Get Info on Preview and toggle this tick box:
so that Preview opens up in 32-bit mode.
TaaDaa now the image will open.
But what if you try to open it in Photoshop CS5?
How's that for helpful?
Oddly, if you QuickLook (Spacebar while it's highlighted) the Finder will preview the image.
So what's going on?
QuickTime Player 7 has an export bug relating to exporting still images from video files. It's some combination of the player, the version of the OS (the bug is less buggy in 10.5.x) and later versions of Preview. I suspect that the way the file is written and/or it's format is deprecated now days and likely has been since 10.4 or thereabouts.
The problem (if you're curious) is how PICT files are constructed. Think of them as PostScript for images in a way. When you run the Terminal command "file" on a QuickDraw picture you'll just see "data" as the result. Which is accurate since the data in the image file is (kinda sorta) just coordinates of how to "draw" that image. Wild, eh?
Now, if a client has handed you a pile of these images what do you do?
Three viable options:
1. Open them in Photoshop CS4 - Not guaranteed to work on a given OS however.
2. Use GraphicConverter - Yes, it's still around.
3. Use Preview by switching it to 32bit mode and then doing a batch convert if you have many of these files. Here's a post about that right here.
Now, you may be asking what the best way to export stills from a video file is? I'd suggest MPEG Streamclip which works nicely and lets you export to formats like TIFF, PNG and Jpeg.