Welcome to MobileRead.
Originally Posted by teddy456
What setting do I need to change to prevent this from happening?
I don't think you can prevent it.
There are sticky posts at the top of each calibre forum that have valuable information for folks using calibre. The following two sticky posts you should read.
How to ask a question about conversion problems
Read this before Posting PDF Questions
If I were to guess, you are converting from PDF and it may be a 2 column format with the pictures in the second column. I don't believe 2 column pdf conversion is currently supported. If it isn't a PDF you may in fact find all of the images at the end of each chapter. If it is PDF your best bet would be to leave it as is.