Meaning of "text user ID's"?

[Peter Lebbing]

(Ah, isn't that nice, Enigmail reformats the message when I do a signature.
Manually restored some sanity)

I'm signing keys after a keysigning party, using GnuPG 2.1.16. Issuing
--edit-key sign, I'm asked:

"Really sign all text user IDs? (y/N)"

Now here's what I see (anonymized):

> gpg (GnuPG) 2.1.16; Copyright (C) 2016 Free Software Foundation, Inc. This
> is free software: you are free to change and redistribute it. There is NO
> WARRANTY, to the extent permitted by law.
>
>
> pub  rsa4096/XXXXXXXXXXXXXXXX created: 2015-10-11  expires: never  usage: SC
> sub  rsa4096/XXXXXXXXXXXXXXXX created: 2015-10-11  expires: never  usage: E
> sub  rsa4096/XXXXXXXXXXXXXXXX created: 2015-10-15  expires: never  usage: S
> [ unknown] (1). Bob Alisson <bob at example.com>
> [ unknown] (2)  Bob Alisson <bob-too at example.com>
> [ unknown] (3)  Bob Alisson <bob-tree at example.com>
> [ unknown] (4)  Bob Alisson <somanyaddrs at example.com>
> [ unknown] (5)  [jpeg image of size 8148]
>
> Really sign all text user IDs? (y/N) y
>
> pub  rsa4096/XXXXXXXXXXXXXXXX
>      created: 2015-10-11  expires: never     usage: SC
>  Primary key fingerprint: [...]
>
>      Bob Alisson <bob at example.com>
>      Bob Alisson <bob-too at example.com>
>      Bob Alisson  <bob-tree at example.com>
>      Bob Alisson <somanyaddrs at example.com>
>      [jpeg image of size 8148]
>
> Are you sure that you want to sign this key with your key "Peter Lebbing
> <peter at digitalbrains.com>" (AC46EFE6DE500B3E)

So how come that the jpeg image is about to be signed as well? What does "TEXT
user ID" mean? I would have expected only the other UID's to be signed. Is this
a bug in my head or in the code?

Cheers,

Peter.

PS: Alice is Bob's forebear.

-- 
I use the GNU Privacy Guard (GnuPG) in combination with Enigmail.
You can send me encrypted mail if you want some privacy.
My key is available at <http://digitalbrains.com/2012/openpgp-key-peter>