How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

Hi all,

I need to insert an image in the buffer in a way that doesn't interfere
with the undo mechanism.  In other words, `insert-image' won't help me
because (as I understand it) it needs to insert a space or some other
string so that it can put display property on it.  How to achieve this?

To be more precise, imagine I have this buffer:

xxxxxxxxxxxxxxxxxxxxxxxx
yyyyyyyyyyyyyyyyyyyyyyyy

(two lines of text).  I want it to look like this:

xxxxxxxxxxxxxxxxxxxxxxxx
+----------------------+
|                      |
+----------------------+
yyyyyyyyyyyyyyyyyyyyyyyy

in other words, I want a rectangular image (inserted by `insert-image'
or actually `svg-insert-image') to appear between them, but in a way
that doesn't actually change the buffer contents.

Alternatively, it _may_ change the buffer contents but in a way that is
not recorded in `buffer-undo-list'.  Is that possible?

TIA,

-- 
Marcin Borkowski
http://mbork.pl