I'm not a LaTeX expert, but I recently used this excerpted bit in a 
metadata file, and it worked for me.  Your mileage may vary.

```
header-includes: |
  \usepackage{graphicx}
  \usepackage{titling}
  \pretitle{\begin{center}
    \includegraphics[height=1.25in]{source/full-logo.png}\Huge\vskip 5em}
  \posttitle{\vfill \color{NavyBlue} \LARGE Long Title of Project
             \par \large PROJECT \par \normalsize Project Agreement No: 
XXXX \par \end{center}}
```


On Friday, 25 December, 2020 at 12:05:33 am UTC+5:30 gnpan wrote:

> Hmm, I don't use Makefile so can't be sure what goes wrong - I put all the 
> fontsize, mainfont, geometry, papersize, etc. in the YAML. Try something 
> simple first:
> Create a test.md file with the following content (or use the attachment):
> ---
> date: 24 December 2020
> header-includes: 
>   - \usepackage{wallpaper}
>   - \addtolength{\wpYoffset}{12cm} 
>   - \ThisCenterWallPaper{1}{WGLogo.png}
> ---
>
> # Your title
>
> Your text. 
>
> Then run this command:
> pandoc --pdf-engine xelatex -o test.pdf test.md
>
> That should work and you can take it on from there. 
> On Thursday, 24 December 2020 at 19:54:28 UTC+2 LRP wrote:
>
>> Oops. I forgot to delete two lines in my YAML  file.
>>
>> error message now reads:
>>
>> Error producing PDF.
>> ! LaTeX Error: Can be used only in preamble.
>>
>> See the LaTeX manual or LaTeX Companion for explanation.
>> Type  H <return>  for immediate help.
>> ...                                             
>>                                                  
>> l.65 \usepackage
>>
>> Here's YAML file:
>>
>> ---
>> ...
>> date: December 23, 2020
>> header-includes:
>>    - \usepackage{wallpaper}
>>    - \ThisCenterWallPaper{1}{WGLogo.png}
>> --
>>
>> Here's -how I call pandoc in Makefile:
>>        pandoc \
>>                 --top-level-division=chapter  \
>>                 --variable mainfont="DejaVu Sans" \
>>                 --variable monofont="DejaVu Sans Mono" \
>>                 --variable fontsize=11pt \
>>                 --variable geometry:"top=1in, bottom=2in, left=1in, 
>> right=1in" \
>>                 --variable geometry:a4paper \
>>                 --table-of-contents \
>>                 --number-sections \
>>                 -f markdown  $< \
>>                 --pdf-engine=pdflatex \
>>                 -o $@
>>
>> Thanks again,
>>
>> LRP
>>
>>
>>
>>
>>
>> On Thu, Dec 24, 2020, at 12:33 PM, Lloyd R. prentice wrote:
>>
>> Thanks. But I get this feedback:
>>
>> [WARNING] Could not fetch resource 'WritersglenLogo_Color.png': replacing 
>> image with description
>> [WARNING] Could not fetch resource 'WritersglenLogo_Color.png': replacing 
>> image with description
>> Error producing PDF.
>> ! Package pdftex.def Error: File 
>> `WritersglenLogo\T1\textunderscoreColor.png' n
>> ot found: using draft setting.
>>
>> See the pdftex.def package documentation for explanation.
>> Type  H <return>  for immediate help.
>>
>> Here's m YAML declaration:
>> ---
>> ...
>> date: December 23, 2020
>> header-includes:
>>    - \usepackage{wallpaper}
>>    - \ThisCenterWallPaper{1}{WGLogo.png}
>> ---
>>
>> And here's my source directory:
>>
>> -rw-r--r-- 1 lloyd lloyd 25516 Aug  1 00:31 WGLogo.png
>> -rw-r--r-- 1 lloyd lloyd   871 Dec 24 12:23 Writersglen.md
>>
>> LRP
>>
>> On Thu, Dec 24, 2020, at 9:43 AM, gnpan wrote:
>>
>> You could use the wallpaper package (
>> https://ftp.cc.uoc.gr/mirrors/CTAN/macros/latex/contrib/wallpaper/wallpapermanual.pdf
>> ).
>> Put the following in your YAML block:
>> header-includes: 
>>   - \usepackage{wallpaper}
>>   - \addtolength{\wpYoffset}{12cm} 
>>   - \ThisCenterWallPaper{1}{logo.png}
>>
>> Change logo.png to whatever you logo is called (make sure it's in the 
>> same folder as your txt file) and adjust the Y offset to a value that gets 
>> the logo in the required position. You can also change the scale factor 
>> {1}. 
>> On Wednesday, 23 December 2020 at 23:38:58 UTC+2 LRP wrote:
>>
>> I'd like to center a logo before the title on my PDF title page.
>>
>> I found a recipe on the web using \usepackage{titling} in the metadata, 
>> but it failed. Can some kind soul show me how?
>>
>> Many thanks,
>>
>> LRP
>>
>>
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>> .
>>
>>
>>
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>> .
>>
>>
>>

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