TImageEnIO.PreviewFontEnabled
 
Declaration
property PreviewFontEnabled: Boolean;
Description
When set to True then you can use 
PreviewFont to specify a custom font for the 
DoPreviews dialogs.
ImageEnView1.IO.PreviewFont.Name := 'Tahoma';
ImageEnView1.IO.PreviewFontEnabled := True;
ImageEnView1.IO.DoPreviews([ppAll]);