The AddPicture method will return an InlineShape object, you can set a variable reference the picture you added, and then play with the properties of the lineshape, like height, width, borders...etc
Code:
Dim header_pic as InlineShape
Set footerPic = ThisDocument.Sections(1).Footers(wdHeaderFooterPrimary).Range.InlineShapes.AddPicture(SrcePath)
With footerPic
.Width = xxxx
.Height = xxxx
End With