The flow to add a randomly-selected image from a OneDrive folder to an email is as follows:

Add a OneDrive get file content action and add the expression
outputs('List_files_in_folder')?['body/value'][rand(0,length(outputs('List_files_in_folder')?['body/value']))]?['Id']

Then in the Send an email action, click the code view </> button and oin the img src line add the expression
dataUri(outputs('Get_file_content')?['body'])

Run the flow and an email will arrive with a random image from the OneDrive folder:

Run it again and a different random image will be in the email:

Rob
Los Gallardos
If I've answered your question or solved your problem, please mark this question as answered. This helps others who have the same question find a solution quickly via the forum search. If you liked my response, please consider giving it a thumbs up. Thanks.