Here’s a quick writing tip for user manuals: don’t add your images to the manual until you’re done writing your text.
This has two advantages. The first is that when you add images one at a time over the long course of writing a manual, it’s easy to overdo it. When you add them all at once, you’re likely to reduce the overall number of images to just right.
The more important advantage is that it will help you write a text that can stand on its own, without the aid of the images. Remember that applications that read out text (for the visually impaired) don’t describe the image, nor are they always very clear when the manual is printed out. Make sure your text can stand on its own.