Is there a way to include a small header image to all pages,
Yes.
How to create a ODT document with a Logo and/or Custom Text in all pages
You need to use the the enhanced ODT exporter ox-odt-9.5.3.456.tar
or later (or simply, any version whose date is later than this comment's date).
The enhanced ODT backend is not available with standard Emacs or Org mode, and you need to install it separately. See Getting Started with ODT export (OpenDocument Text Exporter for Emacs’ Org Mode for instructions.
The snippet is fairly sophisticated set of ox-odt
and Org Babel
features as highlighted in the image below ... So, even if one of the highlighted features aren't enabled, you wouldn't get an output as show below.

See List of features that are exclusive to The Enhanced OpenDocument Exporter for Org mode for more information.
If you need this


do this
Create a header.odt
like so

#+begin_src emacs-lisp :exports results :results silent
(add-to-list 'org-odt-experimental-features 'transclude-sole-footnote-references-in-a-table)
#+end_src
#+ATTR_ODT: :col-cookies "| m1 | rm10 |"
| [fn:1] | {{{ODTTitle}}} |
----------------
[fn:1]
#+ATTR_ODT: :height 1.5
[[./org-mode-unicorn.png]]
Create a content.odt
like so .... note that header.odt
gets transcluded in to content.odt
using a LibreOffice
Basic
macro
#+TITLE: Generate ODT docs with a Page Header and Footer
# #+odt_preferred_output_format: pdf
#+begin_src emacs-lisp :exports results :results silent
(add-to-list 'org-odt-experimental-features 'transclude-sole-footnote-references-in-a-table)
#+end_src
#+begin_src emacs-lisp :exports results :results silent
(custom-set-variables
'(org-odt-transform-processes
'(("Update All and Break Links" "soffice" "--norestore" "--invisible" "--headless" "macro:///OrgMode.Utilities.UpdateAll(%I, 1)"))))
#+end_src
#+name: headertext/org
#+begin_src org :noweb yes :exports none
,#+ATTR_ODT: :transclude t
[[./header.odt]]
#+end_src
#+name: headertext/org/nxml
#+begin_src emacs-lisp :exports none :var name="headertext/org"
(org-odt-export-string-as-odt-string
(org-babel-expand-noweb-references
(org-babel-goto-named-src-block name)))
#+end_src
#+name: footertext/org
#+begin_src org :noweb yes :exports none
,#+ATTR_ODT: :style "Footer"
{{{ODTTab}}}{{{ODTPageNumber}}} of {{{ODTPageCount}}}
#+end_src
#+name: footertext/org/nxml
#+begin_src emacs-lisp :exports none :var name="footertext/org"
(org-odt-export-string-as-odt-string
(org-babel-expand-noweb-references
(org-babel-goto-named-src-block name)))
#+end_src
#+ATTR_ODT: :target "master_styles"
#+begin_src nxml :noweb yes
<style:master-page style:name="Standard"
style:page-layout-name="Mpm1">
<style:header>
<<headertext/org/nxml()>>
</style:header>
<style:footer>
<<footertext/org/nxml()>>
</style:footer>
</style:master-page>
#+end_src
* First Chapter
Anim ullamco enim cillum ea sint sunt qui id nostrud cupidatat
cupidatat irure sed velit veniam, ex. Reprehenderit dolor ut ea
laborum aliquip in enim elit, irure quis eu nulla. Proident, velit id
proident, consectetur adipiscing minim aliqua fugiat incididunt quis
ut dolor minim officia. Deserunt exercitation magna voluptate ea quis
amet, est laboris reprehenderit laborum pariatur est velit ullamco
tempor id commodo sit culpa tempor. Sint culpa cupidatat ut qui elit,
ea veniam, adipiscing nostrud exercitation non pariatur aliquip
eiusmod incididunt cupidatat tempor pariatur tempor.
* Second Chapter
:PROPERTIES:
:ATTR_ODT: :page-break t
:END:
Non exercitation qui esse occaecat ex excepteur duis officia
adipiscing do. Cupidatat aute qui incididunt cillum elit, magna
laborum ex minim ut consequat culpa deserunt ipsum eu aute eu. Eu ex
pariatur nisi duis sit adipiscing lorem ex laborum irure sit laboris
amet, consectetur tempor eiusmod exercitation ex nulla aute commodo
dolor nostrud mollit.
* Third Chapter
:PROPERTIES:
:ATTR_ODT: :page-break t
:END:
Minim est tempor nulla dolore magna anim amet, nostrud. Sed tempor ad
sunt ad fugiat voluptate qui nisi ea ullamco. Nulla incididunt enim
excepteur reprehenderit consequat duis excepteur voluptate enim fugiat
irure. Cupidatat pariatur ut tempor commodo non sit ex adipiscing
anim qui magna incididunt mollit ea ut ut eu laboris commodo do sint.
In magna quis veniam, sunt magna dolor esse do eu ad velit est mollit
anim eiusmod fugiat. Labore non anim nisi cupidatat officia eiusmod
enim qui ad do laborum dolor cupidatat laborum nostrud minim.
#+LATEX_HEADER:
for the LaTeX/PDF exporter, with#+ODT_STYLES_FILE:
for the ODT exporter and with#+HTML_HEAD:
and/or#+HTML_HEAD_EXTRA:
for HTML export). But the contents of those style files are specific to the export format and thus outside the purview of this site.