Not sure about 2007 but I only have 2016. This changes all pictures in a document. Not sure how to modify to cycle through or select one picture.
Code:
Sub ChangeBrightnessAndContrastAllPictures()
'Kilroy
Dim objPic As InlineShape
For Each objPic In ActiveDocument.InlineShapes
objPic.PictureFormat.Brightness = 0.25
objPic.PictureFormat.Contrast = 0.98
Next objPic
End Sub