When stamping images into a PDF, the user has only a limited ability to control the size and positioning of the image within the form field. FDFMerge scales images equally in the horizontal and vertical directions to best fit the fields. It also centers images within the fields so any blank area is evenly divided between right and left or top and bottom. Users cannot specify that they want the image to always touch the upper left corner of the field or that they always want a 50% scaling.
If using a limited number of images, the user can choose the field size and proportion of height and width to best display those images. For example, if all images are scans of 8.5″ x 11″ portrait-oriented pages, the ratio of height to width can be set to 22 x 17, meaning fields could be 66 units high and 51 units wide, or 220 units high and 170 units wide, or any other similar ratio.
However, if using something like a random selection from a clip art library, results are not likely to be consistent.