Best image formats for .pdf?

[Sixteen Coal Black Horses]

Malak's comments are precise.

I've been a pre-press technician for over ten years and I cannot stress enough that one needs to prep art by placing it in one of two categories: Line art or continuous tone.

Line art = minimum of 600 dpi, 1200 dpi is best
Grayscale or Color (continuous tone) = 300 dpi min, 600 dpi best.

Ron also made a great point when he stated that one should strive to get source art produced at the highest possible resolution because art can be downsampled but, for all intents and purposes, cannot be upsampled (Note: there are a number of ways to upsample images, but none are worth the trouble).

Regards,
Doug Woolsey