I have found where to update it on my iPhone in Settings > Mail app > Signature. But there is no way to add a photo other than maybe copying and pasting one? I have tried to paste an image, and it either doesn’t allow me to paste an image at all in the Signature box or when it does allow me to paste an image, it doesn’t actually show up in a test email. There’s just a rectangular box where the image should be.
The iOS Mail app does not provide any explicit way to insert an image in a Signature. Copy and paste an image into the signature from the new email screen is the only method. You should use an image that is already in the Photos app, and make sure it’s no wider than 320 pixels.
Different email readers/clients will have varying behaviors when it comes to images in emails. Most email clients will not automatically show an image that is stored outside of the email itself due to security problems), but they often show images that are embedded in the email itself. Even with that, not every email client will like that (e.g. Gmail’s web interface is pretty strict on embedded images) but it’s typically your best option.
So if you see an empty box on your test email, see if you can try testing again and looking at it from another email program.
Step 1: Use Gmail or (Outlook / Apple Mail on a PC) to create an email, layout the signature as you want, and embed the image/logo you want.
Step 2: Send the email to the account that is on your iPhone.
Step 3: If the email looks OK and you’re happy with the signature then first choose FORWARD to open a new email with the signature visible.
Step 4: Copy the signature from this NEW EMAIL edit window.
Step 5: Go to Settings > Mail > Signature.
Step 6: Create a NEW signature and paste the contents of the clipboard. The image should copy over using this process.
Copy the signature from the email when it comes in does not always pick up the image. The FORWARD then COPY process is more reliable.