The warning you encountered from Ingram could pertain to various images present in your book, such as scene breaks, social media icons, or even bullet points. In most cases, if the flagged images are small or relatively simple in nature, it should not pose any significant issues. However, it's important to pay attention if you have highly-detailed images within your book's content.
To ensure the best possible quality for such images, it is recommended to set them up to appear at a resolution of 300 dots per inch (dpi). This higher resolution ensures that intricate details are preserved and that the images appear sharp and clear when printed.