Hi @Mario17 ,
So, it's an inline attachment, if the image is not very large, you can use the flow I have created below:

expression in Compose:
replace(
outputs('Compose_2'),
concat(
'src="cid:',
outputs('Get_Attachment_(V2)')?['body/contentId'],
'"'
),
concat(
'src="data:',
outputs('Get_Attachment_(V2)')?['body/contentType'],
';base64, ',
outputs('Get_Attachment_(V2)')?['body/contentBytes'],
'"'
)
)
Best regards,