You are seeing emails with embedded images in the signature where attached images are converted to <image001.png> or similar when the email is replied or forwarded from Apple Mail devices.
This issue is caused by a specific setting within Apple Mail, and can be resolved on the client Apple device.
This behaviour is caused solely by the Apple Mail client, and cannot be influenced by the mail sender
The solution to this issue must be performed by the client apple device causing this issue, and can be changed by updating the following setting in Apple Mail.
Settings -> Mail -> Include Attachments with Replies
Update this setting to Always.
By default the Apple Mail client defaults to include attachments When Adding Recipients.