I have a jpeg image that was provided to me for a book cover. The book will be 5.5 x 8.5 inches and the image will be smaller placed in the middle of the page. The scanned image is 8.5 x 11 inches but is only 150 dpi. The publisher would like the image to be 300 dpi. How can I reduce the size of the image and thus increase the dpi? When I tried to reduce the size, it just kept the dpi at 150.