You could do something like this in your page:
<img src="images/myImage.jpg" alt="My Image" width="400" height="300" />
<p class="loading">Please wait while the image loads...</p>
If you give it a width and height, the browser will show a placeholder of the correct size until the image has "arrived." That way the layout doesn't shift or change once the image has been downloaded.
Then make sure jQuery is loaded and then do something like this:
// Do something after images are loaded
Note that this will wait for all images on the page to load. There are other methods to determine if a particular image has loaded, but hopefully this points you in the right direction.