You'd have to code it in, which isn't too hard once you've gotten over the set up hurdle.
https://forum.fenoxo.com/threads/guide-how-to-make-a-mod-for-corruption-of-champions.3283/ - This will tell you how to set everything up.
Once that's done, open
img/images.xml (is the master list for CoC to load images when opening) in the FlashDevelop project and copy and paste a new section with the name of your choice. i.e.
<ImageSet id="gargoyle-girl">
<ImageFile>./img/gargoyle-girl</ImageFile>
<ImageFile>./img/gargoyle-girl_1</ImageFile>
</ImageSet>
Then, you gotta figure out when to display the image. Look in
classes/classes/Scenes/Explore/Gargoyle.as for this example. Each function will usually be a new screen, so after
clearOutput();, write a new line
outputText(images.showImage("gargoyle-girl"), false);
That should be it. Save a new image called gargoyle-girl.png in the image folder and it should load fine.
Side note: The .xml files in the image pack won't update with new mod versions. For up to date versions, check the
img/images.xml file on the mods Github pages.