Knowledge Base

Images in email signatures – linked or embedded?

The HTML format makes it possible to add images to emails and email signatures. Graphics can be included as:

  • linked (online) images, which aren’t a part of an email but are fetched from external locations (servers) when a recipient reads the email. Linked images are referenced in the email's HTML source code by using a URL to an external location, e.g.
    <IMG src="">
  • embedded images, which are a part of an email body. Only local graphics can be used as embedded images - they are added to emails as hidden attachments and are referenced in the email's source code via a Content-ID:
    <IMG src="cid:unique-content-id">

Regardless of which method you choose, we strongly recommend using the most popular image formats, such as JPG or PNG for static graphics and GIF for animated elements, as they are supported by our email signature management solutions and most mail clients. Learn more 

From the table below, you can learn about the advantages and disadvantages of each method.

Linked/hosted/online images
Downloaded directly from server
Embedded images
Included in every message
  • The email size is not increased by images - they are downloaded from a web source when an email is viewed
  • Emails with linked images are rarely blocked by antivirus software
  • You can track who received your email by analyzing web traffic for the images you linked in this message. Learn more
  • Images are displayed automatically when a message is viewed
  • Recipients are never asked by their email client to download images
  • Images are not affected by external factors (e.g. accidental deleting, image URL changes, image server accessibility, etc.)
  • Embedded images are visible when an email client works in offline mode
  • In most email clients, images are not visible until the recipient agrees to download them into the client
  • An SSL-secured server to host your graphics files is required
  • Image availability in email depends on external factors, such as accessibility of the image hosting server
  • Some filters may recognize your messages as SPAM
  • Embedded images increase the message size
  • Emails can sometimes be blocked by antivirus software
  • Embedded images are sometimes removed by mobile devices

General tips on using embedded and linked (online) images in email signatures

In general, embedded images should perform better for most common email signature scenarios. They are an integral part of an email, which makes them more reliable – your recipients don’t need to perform any additional actions to see your email signatures exactly the way you designed them (Fig. 1.). That’s why, it’s a good idea to add you company logo, social media icons, or marketing banners as the embedded images. These elements are usually not that big in size (e.g. less than 0.5 MB), so your emails should not increase that much in size.

Email signature with embedded images (left) and with linked/online images (right) – to see online images, your recipient must click the highlighted message first.
Fig. 1. Email signature with embedded images (left) and with linked/online images (right) – to see online images, your recipient must click the highlighted message first.

On the other hand, linked/online images are a better solution if you are concerned about the size of your emails. For example, you want to add a high-resolution image to show off your product directly in your email signature, and the image is big in size (e.g. above 1 MB). In such a case, adding an online image that links e.g. to your server/website is a better idea to avoid clogging your and your recipients’ mailboxes with large amounts of data, which is not that difficult even if you don’t exchange a great number of emails.


With CodeTwo signature management software, you can add email signatures with hi-res images only to the first email in a conversation and use a simplified signature in all subsequent emails. Find out how to achieve that in:

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