[lmikle]

Сделай полный путь:

Код:

var
  AFileName : Stirng;
begin
  AFileName := IncludeTrailingPathDelimiter(ExtractFilePath(Application.ExeName)) + 'source\posters\' + ListBox1.Items[ListBox1.ItemIndex]+'.jpg';
  If Not FileExists(AFileName) 
   Then ShowMessage('File not found: ' + AFileName)
   Else img4.Picture.LoadFromFile(AFileName);