When we are using a GridViewSelectColumn in a RadGridView, the CheckBox is displayed using the Silverlight theme, not the current Telerik application theme.
You can see an example this in the Column Type
demo on your site, which uses the Metro theme, but not for this column. To see the difference, open the filter for the Photo column, which displays the CheckBoxes correctly.
Also there is no sense to have a filter on the photo number!