Images within InDesign file getting corrupted

[#1]

I'm new with Adobe CC. Recently, I inserted (Ctrl + D) about 40 illustrations into an InDesign file. When I opened the same file a few days later, I found two illustrations pixelated (or corrupted). One heavily, another mildly. I wonder what might be the reason. It's been an unwanted hassle replacing these illustrations. Below is a image before and after the corruption:

Before corruptionAfter corruption

[#2]

First, check the display performance in the View menu: is it on Typical or High quality?

[#3]

Thanks for the question. It was High quality. It's to note that both the images that I shared in this thread are taken from 2 pdf files created out of the same Indesign file with a gap of a few days. So, it's not the matter of View > High Quality.

[#4 · Accepted solution]

Check the Links panel.

[#5 · Accepted solution]

Thanks. Now I know the underlying reason. It's all in the links. I didn't even know that unlike Photoshop or Illustrator, the contents in any given InDesign file actually link to the files in other locations and when I delete or move something from the original location, InDesign is unable to show it. It's all in the links!!!