Sended WM_PASTE Message does't work

I want to paste an image to a window of Accessories/paint.On the assumption that an image has already in the clipboard, I wrote some code like this in the follow,but it doesn't work.Do you have some advices?
...
HWND hWnd=NULL;
hWnd=::FindWindow(NULL,TitleName); //TitleName is for paint window
if(hWnd==NULL){
AfxMessageBox("not found window");
}
BOOL bRes;
bRes=::EnumChildWindows(hWnd,myfunc,(LPARAM)0);
...

BOOL CALLBACK myfunc( HWND hwnd,LPARAM lParam )
{
if(hwnd!=NULL)
::SendMessage(hwnd,WM_PASTE,0,0);
return TRUE;
}

Regards,
Susan