I've tried center anchoring it but it still upper left justifies any image inserted in the image field.
I normally use the old Text Field Trick in LiveCycle.
Create a new Text Field, Set your Text Justification Options and then change the Field to Image Field.
It will retain the Text Field Settings from before.. Used that "trick" many times.
this.para.vAlign = "middle";
this.para.hAlign = "center";