DPI, PPI, Pixles? What?

Oh dear, sorry but there is something you must know. First of all, you can't change an image's dpi. The only thing you can change in an image editor is the ppi - which for all intents and purposes most image editors treat as though it was dpi. But increasing or changing the ppi is an utterly pointless exercise. Let me explain why. The ppi or dpi is actually irrelevant. All that matters is the size of your image in pixels, and whether or not there are sufficient pixels in your image to print a quality image at the required size at 300 dpi (which is the printer resolution). Here's how to work out if your image is big enough in pixels to print at 300 dpi. Lets say you have one image on your A5 page which will be reproduced at 3 x 2 inches. At 300 ppi that means you will need an image that is 3x300 by 2x300 = 900 by 600 pixels. So if you wanted to crop it to that size it would be fine. Don't worry about setting the ppi, it's irrelevant and will make no difference. Just make sure when you save the file from your DTP software that it is creating the PDF at the proper resolution. Depending on the software, there will a setting for this somewhere.