I read your post with great interest and did some tests myself using images taken from a small Canon Ixus and it's big brother EOS 7D. The aim was to see how much an image could be resized without losing too much resoution quality on an HP ColorLaserJet.
I spotted the Ixus picts where at 180 dpi (4000x3000 pixels) while the 7D's are at 72 dpi (5184 × 3456 pixels). So resizing will only affect the physical dimensions without touching the image resolution.
Do you or anyone else has a hint or an idea how to resize an image but increase their resolution.
Let's say that the 72 dpi image @ 5184 × 3456 pixels would be ideally resized to 288 dpi @ 1296 x 864 pixels.
Sorry, Guy. No idea how you might change the dpi of a photo through filemaker or otherwise.
I will say generally, however, that when it comes to printing, I don't think the dpi really factors in. I'm certainly no expert on digital photos, but I think that dpi (dots per inch) is only a measure of interest regarding on-screen display, whereas pixel resolution is what you're concerned with when printing photos.