Each (color) image is composed of RGB components. when you add (or reduce) a constant value to all pixels only in RED components you will see the effect equivalent to moving the RED tab towards the right, and same way reducing the RED component by a constant will have the reverse effect.
Like wise you can increment/decrement each component by a fixed value ...
You can't. If an attacker can insert a signal that covers the whole bandwidth (e.g. a white signal, or at least one that has no spectral zeros) into the system (and he can do that over an arbitrarily long time, or add up observations), they will get an output, and can through the magic of correlation get the impulse response.
Let's model the information flow from your "hidden" IIR $X$ to your observable output $Y$ as
$$ X \longrightarrow Y$$
Then, we call the amount of information you get per observation the *mutual information $I(X;Y)$; that information is the reduction of uncertainty about $X$ to be achieved by observing $Y$.
We call the expected uncertainty ...
Convolution is a linear operator. As such, it can be, at least theoretically, inverted. But it is infinite in length, and in coefficient amplitude precision. Which, in real world practice, cannot be reached.
So the balance resides in what you call "protecting", and there might be some "privacy by design" possibilities:
if the algorithm is a mere ...
There are many algorithms for "edge-aware" upsampling. Not sure what Photoshop itself uses, but for example Alien Skin Blow Up plugin gives similar results and they use vectorization using triangulation. The triangles are carefully smoothed while keeping the upsampled image sharp enough.
You can also take a look on NEDI (New Edge-Directed Interpolation), or ...
It's really nothing beyond Bi Cubic Interpolation with "Sharpening".
They haven't updated their interpolation algorithms for ages.