So I wanted to take advantage of adding screenshots to my tickets using markdown, but I didn't have an image host or anything to upload my screenshot to.
I had been adding them and pointing customers to the Attachment(s) at the bottom of the email. Now, only since this wasn't as blatantly obvious for me as I thought it should be, I thought I'd share my findings...
If you'd like to upload an image and use it as an embedded image like you would do in markdown, simply drag-and-drop or attach your screenshot to the ticket. Then, right-click the attachment at the bottom and copy the URL and use this to embed your image.
This helps avoid the need for a third-party image host. I've tested this in case there were restrictions on viewing the image and the end user can see it fine.
Zendesk note: We love this tip! But please note this tip does not work if you have Private Attachments enabled (Admin > Tickets > Attachments).
Also, make sure you click the attachment link in the ticket to open the attached image in a modal box. Then, right-click the image and select click Copy image URL. Do not click on the image link before opening the attachment, which opens a new browser tab. The URL in the new browser tab will not work, as this includes a temporary token.