How can I apply contrast & brightness settings to all photos in a document?

A similar macro will set all the pictures, both inline and floating, except for any that have already been modified through either the Picture Tools > Corrections gallery or the Format Pictures dialog:

Sub ReproPhotoSettings()
    Dim newBright As Single
    Dim newContrast As Single
    Dim ILS As InlineShape
    Dim shp As Shape
    
    newBright = Val(InputBox("Enter brightness (-100 to 100):", _
        "Brightness", 0)) / 200 + 0.5
    newContrast = Val(InputBox("Enter contrast (-100 to 100):", _
        "Contrast", 0)) / 200 + 0.5
    
    For Each ILS In ActiveDocument.InlineShapes
        With ILS.PictureFormat
            .Brightness = newBright
            .Contrast = newContrast
        End With
    Next
        
    For Each shp In ActiveDocument.Shapes
        With shp.PictureFormat
            .Brightness = newBright
            .Contrast = newContrast
        End With
    Next
End Sub

The bug, which appears in both Word 2010 and 2013, has disconnected the picture format controls in the user interface from the PictureFormat object in the macro language -- neither one can see any changes made by the other. If you want to affect all the images in the document, they all have to be reset (use the Reset Picture button on the Picture Tools tab).