There are some important factors to note while embedding images:
The Kindle eBook format supports JPEG and GIF interior image files (maximum 5MB).
Kindle Direct Publishing converts image files along with text content. Kindle Direct Publishing can process graphics in the following formats:
GIF (or .gif)
PNG (or .png)
BMP (or .bmp)
JPEG (or .jpeg)
Prefer saving your images in JPEG format, as it offers a good compromise between size and quality. PNG and BMP files can be larger in comparison to the other size formats. GIF files have many built-in limitations. In JPEG format, if you are unable to upload your images, prefer GIF format as second choice.
Any vector graphics like SVG are not supported in Kindle books.
Preserving image aspect ratio:
While defining height and width of image, prefer to set any one of them as auto to preserve aspect ratio of image.
Prefer %(percentage) instead of px(pixel) for defining dimensions of image so as to keep image resolution similar for all supported devices.