1)image from static folder
xxxxxxxxxx
<img class="img" src="/your_module/static/src/img/your_image.png" style="height:45%;width:100%;" />
2)Image from database
xxxxxxxxxx
<img t-att-src="'data:image/png;base64,%s' % to_text(doc.yor_field_name)"/>
xxxxxxxxxx
<div class="text-center">
<img src="..." class="rounded" alt="...">
</div>
https://www.odoo.com/forum/help-1/how-can-i-add-a-background-image-to-reports-93758