The proof photos of the last items for the latest book are coming back soon. I'm looking forward to seeing them as my own photos, whilst they look good when I take them, never match the great quality of the professionally taken ones.
The illustrations make such a difference to a (and I hate to use this word) 'craft' book. I've worked on quite a few, and had very different experiences.

• taking my own (difficult setting up space with good lighting, not having professional kit, limited knowledge of photography)
• with a semi-professional at home with minimum studio kit (OK experience - although the dogs were a bit of a bind, but the lighting was not good, and the final photos dull)
• with a professional photographer in a commercial studio (exhausting and exacting expereince, great images; strong, vivid and clear, if a little sterile)
• on location with stylists, models and a professional photographer with all the kit (periods of intense boredom whilst everything is shifted around, lighting sorted etc,  freezing cold, lots of lugging equipment about and a challenge keeping knitting neat on location, interesting and well lit photos)
• in a professional photographer's own location-based studio (aesthetically exacting, able to be more flexible, easier to keep knitting looking good, marvellous exciting images).

From this I guess you can tell which I thought was the most rewarding experience. However, the photos were for different purposes, some were for pattern book illustration, and some for technical knitting, so may not be fully comparable.

It is clear to me that the 'author takes photos' option has the following disadvantages:

a) can be challenging and often inappropriate for the author's skillset
b) more often than not, results in poor quality images

But it has the following advantages:
a) author retains control of content
b) cheap for the publisher - whether a commercial publisher or self-publishing


As a further observation, it is crucial for good 'how to' books to have big pictures. In the example I mention above, of using semi-professional photos taken at home, the poor quality of the photos was compounded by the layout design cramming them into small frames at the side of text.  At first I thought these should have been cropped so that more detail showed, but realistically the photos were original framed poorly so that they couldn't be cropped without loosing content/context - hence the disadvantages of not using a professional photographer.
Having said all this, I am sure some authors take brilliant images and use them very well in books, these are just my personal experiences and observations. I suppose its a moan to publishers really, if they want a great 'how to' book, they need to invest in good photography and give space in the layout for images to be large enough to warrant their investment.
So my advice to other authors (for want its worth), is to persuade your publisher to shell out for professional photography and illustrations whenever and wherever possible.