This will be almost impossible. The short answer is that those pictures might be 95% similar but their binary data might be 100% different.

Long answer:

Images are essentially a long list of pixels, each pixel is 3 numbers for Red, Green and Blue (and optionally Alpha if you're dealing with a transparent image, but you're talking pictures so I'll ignore that). This is a simple but very stupid way to store the data of an image, because it's very likely that the image will use the same color in multiple places, so you can instead list all of the colors a image uses, and then represent the pixels as the number in that list, this makes images occupy a LOT less space. Some formats add to that, because your eye can't see the difference between two very close colors, they group all colors that are similar into one only color, making their list of colors used on the image WAY smaller, thus having the entire image be a LOT more compressed (but you might noticed we lost information in this step). Because of this it's possible that one image choose color X in position Y, while the other choose Z in position W, the binaries are now completely different, but an image comparison tool can tell you that color X and Z are similar enough to be the same, and they account for a given percentage of the image depending on the amount minimum of the values Y and W. But outside of image software, nothing else knows that these two completely different binaries are the same. If you hadn't loss data by compressing get images in the first place you could theoretically use data from different images to compress (but the results wouldn't be great, since even uncompressed images won't be as similar as you think), but images can be compressed a LOT more by losing unimportant data so the tradeoffs are not worth it, which is why JPEG is so ubiquitous nowadays.

All of that being said, a compression algorithm specifically designed for images could take advantage of this, but no general purpose compression can, and it's unlikely someone went to the trouble of building a compression for this specific case, when each image is already compressed there's little to be gained by writing something that takes colors from multiple images in consideration, needing to decide if an image is similar enough to be bundled in together with that group or not, etc. This is an interesting question, and I wouldn't br surprised to know that Google has one such algorithm to store all images you snap together that it can already know will be sequential. But for home NAS I think it's unlikely you'll find something.

Besides all of this, storage is cheap, just buy an extra disk and move over some files there, that's likely to be your best way forward anyways.

No, it is impossible to solve this on filesystem level. In theory, it would be possible to adopt some video codec for compression of such photo series, but it would be a lot of work to integrate it into immich.

we can have 5~10 photos which are basically duplicates

Have any of you guys handled a similar situation?

I decide which one is the best and then delete the others. Sometimes I keep 2, but that's an exception. I do that as early as possible.

I don't mind about storage space at all (still many TB free), but keeping (near-)duplicates costs valuable time of my life. Therefore I avoid it.

No that’s really not possible. I’d recommend tossing the similar ones after you pick the “best”.

Not sure if a de-duplicating filesystem would help with that or not. Depends, I guess, on if there are similarities between the similar images at the block level.

Maybe try setting up a small, test ZFS pool, enabling de-dup, adding some similar images, and then checking the de-dupe rate? If that works, then you can plan a more permanent ZFS (or other filesystem that supports de-duplication) setup to hold your images.

Well how would you know which ones you'd be okay with a program deleting or not? You're the one taking the pictures.

Deduplication checking is about files that have exactly the same data payload contents. Filesystems don't have a concept of images versus other files. They just store data objects.

Storage is cheap. You suggest combining the images and storing the difference.

You can't separate the images anymore. You have to store them in a container such that you have one common base image. You can then later on decide which image to look at.

You could also take a short video and only display one image.

Avif uses a video compression algorithm, meaning it's basically one frame of a video.

Btw, I wouldn't care about your problem. Storage is cheap. Try saving 10 4k videos and you'll laugh about your image library

Not sure if you're aware, but Immich has a duplicate finder

Compression?

When do you do the choosing? Try move that left in the process. Saving storage.

That basic idea is roughly how compression works in general. Think zip, tar, etc. files. Identify snippets of highly used byte sequences and create a “map of where each sequence is used. These methods work great on simple types of data like text files where there’s a lot of repetition. Photos have a lot more randomness and tend not to compress as well. At least not so simply.

You could apply the same methods to multiple image files but I think you’ll run into the same challenge. They won’t compress very well. So you’d have to come up with a more nuanced strategy. It’s a fascinating idea that’s worth exploring. But you’re definitely in the realm of advanced algorithms, file formats, and storage devices.

That’s apparently my long response for “the other responses are right”

I went through the same dilemma. The old Synology photo software had a duplicate finder, but they removed that feature with the "new" version. But even with the duplicate finder, it wasn't very powerful and offered no adjustability.

In the end, I ended up paying for a program called "Excire Foto", which can pull images from my NAS, and can not only find duplicates in a customized and accurate way. It also has a localAI search that bests even Google Photos.

It runs from windows, saves its own database, and can be used as read-only, if you only want to make use of the search feature.

To me, it was worth the investment.

Side note: if I only had <50,000 photos, then I'd probably find a free/cheaper way to do it. At the time, I had over 150,000 images, going back to when the first digital cameras were available + hundreds of scanned negatives and traditional (film) photos, so I really didn't want to spend weeks sorting it all out!

Oh, the software can even tag your photos for subjects so that it's baked into the EXIF data (so other programs can make use of it).

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

3 acronyms in this thread; the most compressed thread commented on today has 9 acronyms.

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File system deduplication might be best bet, though I don't know what's the potential.