Epson Perfection V500 - Manual (Page 68)

Depending on your document type and other settings, the normal preview may be
automatically selected and you will not be able to change to thumbnail preview.
Follow these steps to preview your image(s) in Home or Professional Mode.
Click the Preview button toward the bottom of the Epson Scan window. If you want to
change the preview type, click the Thumbnail checkbox under the Preview button, if it is
available.
Epson Scan prescans your image(s) and displays them in one of the following Preview
windows.
Normal preview