You could basically use anyone of these:
Code:
Client control functions
procedure FindWindow(Title: string);
Finds Client window with specified title. Character case of Title must match that in window title exactly.
function FindWindowTitlePart(Title: string; CaseSensitive: Boolean): Boolean;
Finds window that contains text specified by Title parameter in window caption.
function FindWindowBySize(Width, Height: Integer): Boolean;
Finds window with specified size.
function GetClientWindowHandle: Integer;
Get Windows handle value of active client window.
procedure SetClientWindowHandle(H: Integer);
Set active client window to handle H.
Example:
H:= GetClientWindowHandle;
//specify another client window
FindWindow('Debug Image');
...
//return to previous client
SetClientWindowHandle(H);
procedure GetClientDimensions(var Width, Height: Integer);
Get client width and height.
I would go with FindWindowBySize..