Kindle previewer - images not resizing to page width

[goodmorningjulie]

Hi everyone,

My client is uploading her mobi that I created to Amazon and while the mobi looks fine on my physical Kindle, in the online previewer the images are not resizing to suit the current width of the text on screen.

I've attached screenshots of what she is seeing.

There are probably 100 images in the book

Does anyone know right off the bat exactly why the previewer is seeing it this way? Is there a line of code that I could add to the ebook that would resolve this on this device (and in case it happens on any others?) I can't force all the images to be one size/width because they are various widths (some are pull quotes that are 50% width, some are cartoons that are 100% width, etc).

Thanks in advance for helping me in my ignorance!

Julie