Images with same name cannot be compared.

[IvanT24]

When loading an image with the same name as an already loaded image, it will be overwritten. I wanted to compare images with the same name built in two different environments, but i had to first use the docker tag command to change the name of one of the images before I exported it.

[omus]

Does using the digest hash work? e.g. debian@sha256:45f2e735295654f13e3be10da2a6892c708f71a71be845818f6058982761a6d3. You can determine the digest for your images with docker image ls --digests <image>.

[Antiz96]

[...] but i had to first use the docker tag command to change the name of one of the images before I exported it.

For what it's worth, this is not a fully satisfactory solution as "renaming" an image with docker tag will reflect said rename in the image annotations metadata (in io.containerd.image.name & org.opencontainers.image.ref.name), which diffoci will complain about (if not ran with the --semantic flag).

See for instance the following diffoci output (with the difference being introduced by using docker tag to "rename" one of the images with the "-rebuild" suffix, in order to avoid name collision).

- 	"org.opencontainers.image.ref.name": "repro-repro",
+ 	"org.opencontainers.image.ref.name": "repro-repro-rebuild",

I tried to find a way to either rename / retag the image while preserving the original annotations metadata or, alternatively, find a way to edit the annotations back to their original value afterwards but I haven't been able to find a solution / workaround for that yet 😕

Note that I'm not implying that this is an issue with diffoci, I'm aware it's just doing its job here 😛
More of a limitation of the Docker / Podman image format I guess.