Copy the file /usr/dt/examples/types/language/IconBrowse.dt into your /$HOME/.dt/types folder.
Open Application Manager and double-click Reload Actions in the Desktop_Controls application group.
Restart File Manager.
The maximum default display area for icons is 38x38 pixels. So, if a picture file is larger than 38x38, the picture will be clipped and only the top left 38x38 pixels will be shown. You can increase the size of the display area for icons if you want larger images to be fully visible (see "To Change the Icon Display Area Size"). However, a larger display size area will slow down the opening of folders, and icons will be spread further apart in folder views.