I don't think that Pinterest has a better algortim than google/youtube
But it all depends what kind of image you wanna create/modify.
You might be right in terms of complexity, but you forget the key area which is that Pinterest is geared solely towards images alone and is an image search engine/cataloging system built from the ground up.
In answer to OP, Sure you might feel changing the light or contrast of the image, or perhaps even the image hash (MD5) is a good approach, and in some instances, you would be right and you may even get the desired results in terms of engagement or click-throughs.
However, there is a key difference between an image that "IS the same" and modified, and an image that "IS different" due to modification. To even attempt to explain this fully would take a thread of its own, but this can quickly be observed using Pinterest's own image search (Visual Search).
If you were to save an image from Pinterest such as a "Brown Dog" which is an image of a brown dog in a green grass field.
You then modify this image using any manner of filters or adjustments such as contrast, lighting exposure or even adding CTA text onto the image in the lower or upper portion.
You also may choose to change the image hash or identifiers.
You post this back onto Pinterest.
Quite often after the algorithm has had enough time to index this, in the related pins or using "Visually similar results" you will re-find the original or someone else's reiteration of this image.
This suggests that perhaps to make a more unique image would require heavier modification taking it out of the bounds of what Pinterest "Knows" and the algorithm.
Things such as image rotation, background removal, color replacement or any other method to break or remold the original structure of the image so that it can not be distinguished from the original or inherently does not "LOOK" the same.
i.e You could change the Brown Dog into a Black Dog, you could change the background entirely, you could rotate the dog and move the dog's legs position or stance.
While this is by no means an easy task and would be one hell of a project to automate, it can be achieved manually with some effort (which I would not wish on anyone to undertake solo for multiple Pins/Accounts).
With the example of the "Brown Dog" in mind however, there is a middle ground that can be achieved and automated.
Using Photoshop, Free online image editors similar to Canva, or your own personally developed tools.
You can preset that "Brown Dog" image to, once loaded in be automatically processed with as many modifications as possible such as rotation, cropping, resizing, color adjustments, borders, and a combination of CTA text, overlaying text or designs, or text describing the image or target URL.
This can be achieved using anything from free Macro's that run within the browser on a free photo editor site to more advanced personally developed tools that are more costly a run on your own web servers passively.
It can be trial and error for sure in the beginning, but there are many options to go forward with image manipulation especially for many pins, or bulk processing of pin images. While there is no guarantee in the eyes of Pinterest that your image will be unique, at least you are making the steps available to you in order to pursue this and learning from the process.
The image sources you use should also be considered heavily. As if an image has never appeared on Pinterest it's inherently unique already. So finding areas online that stock many (unknown in the eyes of Pinterest) images for your niche or target domain could be valuable to know.
The key initially is to know the path you will take on your Pinterest accounts, will you need a lot of images per week or a few images per week? This will help you gauge the level of automation and image modification that may be required for your accounts longevity and growth. With consistancy being a key factor. It also helps you better manage your time away from image management which could be better served to create new accounts, outsourcing content, etc.