There are 2 ways images can be attached in emails on Canary for macOS: 1) As attachments 2) Inline. Canary only displays actual inline images as inline.
While writing or replying to an email, click on the attachment icon.
1) Choose the files you want to attach. To select multiple files at once, hold Cmd.
2) Click Open.
Note: Canary uses an attachment size limit reported by the server. If your files are larger, we recommend you upload them to cloud storage and paste the link in your email.
3) To remove the attached file, click on the cross icon.
1) Choose Attachments as usual.
2) Drag and drop the attachments to the body of an email.