Adding a cover may change the length

Once I add a cover into a mp3 file, Mp3tag may extend its length probably, the bigger cover file is, the longer mp3 file I will get.
I'm using Mp3tag v3.02

By "length" do you mean "playing time" or "size in bytes"?

If the playing time increases: how do you know? Where do you see that increase?

I mean "playing time", I made a copy before adding the cover, so I could compare edited one with the original one, I played them with both Potplayer(Windows) and smartphone(Android), and get the same result.
Such things happened frequently after I updated Mp3tag to v3.02 but never in older version.

But the display of the length in MP3tag does not change?
I would test these files with the linked tools:

and see if there is a cause why the players interpret the covers as music data.

No. Thanks for your work, I'll be waiting for ya.

I don't understand. Do you expect me to

as I wrote

You have to test them. And try to repair them.

Sorry, I misunderstood what you said.
I just tried mp3val, it didn't work at all.

The 3 tools serve different purposes and are good at different disciplines. So you probably would have to try them all.

Thank you, I just missed the other two.
Problem solved, MP3 Diags>Apply a single transformation>Remove unsupported streams, then I got a mp3 file with cover art and original length.