Photo gallery user control
the variable holding the DirectoryInfo object should be named using lower case.  
you should always use Sytem.IO.Path.Combine() to combine a folder with a filename.  
you could use DirectoryInfo.EnumerateFiles combined with the Select() and assign the returned IEnumerable to the DataSource property of the Repeater control.
you should add spacing to the property FolderPath. Instead of  

public string FolderPath {get;set;}  


you should use  

public string FolderPath { get; set; }  

Repeater1 is an ugly name which isn't decsriptive either. Change it to something more descriptive.