Canon 10D User Guide (en)

Viewing an Image
Images downloaded to your computer are displayed as a thumbnails list 
in the main window. You can double-click an image to open the edit 
window and display the image at large size.
View Images as Thumbnails in the Main Window
Main window
Rotate selected image
Click to select the image
Display thumbnails of all the images inside the 
folder selected in the folder area on the left
When aspect ratio information is attached to the shot image with 
a camera where you can set the aspect ratio, the image is 
displayed as a trimmed image 
For a list of main window functions, refer to 
Changing the Size of Images
You can change the size of the thumbnail images displayed in the main 
window and display them with shooting information attached.
Select the [View] menu   desired item.
The display changes to the selected item.