Why is my subtheme screenshot not appearing? I have created a subtheme, and it shows up correctly on the admin/appearance page, but I can't seem to get my screenshot to appear.  It only displays the screenshot from the base theme.  I have declared the screenshot in mytheme.info, and the PNG file is sized to exactly 294 x 219.  Any ideas?

Thanks!
Sub theme by default inherit the screenshot from base theme.You can override the screen shot by simply adding screenshot of your sub theme in your sub theme directory


  The optional screenshot key tells Drupal where to find the theme's
  thumbnail image, used on the theme selection page
  (admin/build/themes). If this key is omitted from the .info file,
  Drupal uses the "screenshot.png" file in the theme's directory.
  
  Use this key only if your thumbnail file is not called
  "screenshot.png" or if you want to place it in a directory outside of
  your theme's base directory (e.g. screenshot = images/screenshot.png).


screenshot = screenshot.png


Reference: https://drupal.org/node/171205#screenshot

Other things which may help.


As Jhilke comment try clearing your caches.
Check the screenshot file permission it should readable by web-server.