How do I attach photos to emails?

This right here was the answer. It's about the signature. Must be text only.

After re-reading this thread I believe the issue may be due to the fact that there are actually two ways to email photos from an iOS device, and the difference is what explains if the photo is embedded or attached:

1- If you open the Photos app, tap the arrow in the lower-left corner and select the option to e-mail the photo, it will be as an attachment.

2- If you start an e-mail message (or are replying to an existing one) you can insert a photo into the message by doing a long-press in an empty area within the message. Then when you see the pop-up, tap the arrow on the right and select "Insert Photo or Video". Doing this will send the photo as an embedded image. The recipient can easily save the image as a separate file by right-clicking on it when viewing in Outlook (i.e. "Save as Picture").

I use no signature at all and the above behavior is how iOS has always behaved in my experience (though I don't remember exactly when #2 became possible).

rockmyplimsoul wrote:

1- If you open the Photos app, tap the arrow in the lower-left corner and select the option to e-mail the photo, it will be as an attachment.

I played around with creating a signature and gbumoon is correct ... if your signature has font alterations (bold, italics), hyperlinks, or even empty lines after your signature, then e-mailing a photo from the Photo app will embed the image instead of sending it as an attachment.

So that is likely the difference between attachments or being embedded (but method #2 above is another difference).