user24084: My comp setup is as follows:
- layer 1: image
- layer 2: duplicated from layer one
I'm looking for an expression or any other method (Could be a plugin recommendation) so when I change the image of layer 1, it automatically updates layer 2!

user4426: It depends how you mean: 
Option 1:
If you put the image in Layer 1 inside a Comp, then any change to the image inside the Comp will change in both Layer 1 and Layer 2 (assuming you also put the Comp on Layer 2).
Option 2:
You could put a load of different images inside a comp, a different one on each frame.
Then in your master comp, place this comp, but assign Time Remap to the comp, to choose to hold on a specific frame.  Then when you want to change the held frame, just keyframe to the different time in your first comp.
Option 3: 
If you really mean to change the image programmatically, you could use something like Templater Rig, where you can set a load of different file paths to images, and then assign them to different comps programmatically.

24084: <p>My comp setup is as follows:
- layer 1: image
- layer 2: duplicated from layer one</p>

<p>I'm looking for an expression or any other method (Could be a plugin recommendation) so when I change the image of layer 1, it automatically updates layer 2!</p>
 4426: <p>It depends how you mean: </p>

<p>Option 1:
If you put the image in Layer 1 inside a Comp, then any change to the image inside the Comp will change in both Layer 1 and Layer 2 (assuming you also put the Comp on Layer 2).</p>

<p>Option 2:
You could put a load of different images inside a comp, a different one on each frame.
Then in your master comp, place this comp, but assign Time Remap to the comp, to choose to hold on a specific frame.  Then when you want to change the held frame, just keyframe to the different time in your first comp.</p>

<p>Option 3: 
If you really mean to change the image programmatically, you could use something like <a href="https://aescripts.com/templater/" rel="nofollow noreferrer">Templater Rig</a>, where you can set a load of different file paths to images, and then assign them to different comps programmatically.</p>
