Selecting how camera images show up in a PDF form can be done by going into the Form Template that you would like to edit/adjust, and then into the PDF > PDF Settings.

By default each photo field will be 3 per row on the PDF. You can change this in the PDF Settings of the form template. Element > + New Element to create an element or edit an existing one, and then choose Photo from the dropdown. It will then come up with a list of items, one of them being the number of photos you would like per row. Here you can choose how many you would like, and they will all adjust to be equal sizes automatically in the form when you add images via a Camera/Photo field in the form. You can also target all photo fields or each photo field individually.

Remember to save the settings before closing the PDF Editor for this to work.