I created a PNG file (763px by 600px at 72DPI) from a free image. I opened the image in GIMP and changed the DPI to 300 and saved it. After including it in a LaTeX file with
pdflatex, the image looked good on the page. I wanted it a little bit larger, so I changed the DPI in GIMP to 600 and saved the file. After recompiling the source, the image is now much smaller on the output PDF. What have I done wrong?