Which images to use in email signatures – linked or embedded?

Images have become a necessity in email signatures. Banners, logos, social media icons… I’m sure you’ve seen dozens of signatures full of those. To include them in your signature, you first need to add them somehow. And that’s where the story of linked and embedded images begins.

Linked vs embedded images: what’s the difference?

This dichotomy is about how you add an image to an email signature:

• A linked image (aka online/hosted/hotlinked image) is stored in an external web location (e.g. your CDN, website, Dropbox, Imgur, etc.). You reference it in your signature by providing its direct URL (web address). It isn’t a ‘local’ part of your email signature. When your email is received, the recipient’s email app accesses the image’s web location and displays the image from that remote location.
• An embedded image (aka inline/local image) is a local image that you add directly into the email. As the name suggests, once added, it becomes embedded into your signature, making it a true part of it. There are two different kinds of embedded images – CID images (or hidden attachments) and BASE64 images, but more on that later.

What are the pros and cons of linked and embedded images?

Review the advantages and disadvantages of both methods for adding images to an email signature to help you decide which approach to take.

Linked images

Pros:

• Do not increase the size of emails.
• Easy to update, even after emails are sent – just replace the image on the server.
• Often used to track email deliverability or the number of image impressions (how many times an image is displayed to recipients).

Cons:

• Blocked by default in most email apps; images become visible after the recipient agrees to download them or if you’re on their Safe Senders list. This is commonly known as the ‘red X’ issue:

• Modern email security solutions are generally suspicious of links, which may result in your emails being blocked on the recipient’s side.
• Whether an image is displayed correctly in the recipient’s inbox, depends on the availability of external image hosting services (e.g. Flickr) or servers.
• Take special care to use (and reference) a secure HTTPS location. If your linked image’s source begins with “http://” instead of “https://”, most spam filters will block your email immediately, even if a redirect to a secure location exists. Learn more about email signatures vs spam

Embedded images

CID (content ID) images or hidden attachments

First, a bit of theory. After you add a local image to your signature, every time you write an email with the signature, the image is attached as a hidden attachment and assigned a unique content ID (CID), becoming the part of the email.

Pros:

• Display automatically in the recipient’s email app, with no prompts to download images.
• Visible offline, as neither your nor your recipients’ email apps need to download images from an external location.
• Image availability isn’t dependent on external factors.

Cons:

• Increase email size, potentially clogging mailboxes if images are not optimized (e.g. by resizing large logos, icons, or banner images).
• Some email apps, such as Apple Mail, may remove embedded images or restore their original size when replying.

BASE64 images

BASE64 is an image encoding format. It’s used to convert an image into a text string, which can then be added (embedded) directly to the HTML code of an email signature, becoming an inseparable part of it.

BASE64 images share similar pros and cons with CID images, but with a twist:

• Some security policies block BASE64-encoded images.
• Not all web-based email apps display them.
• Adding them to an email signature can be tricky.
• Some spam filters are allergic to those images.

Which image type to use?

The answer is super simple: it depends.

When to use embedded images?

If you ask me about images in email signature best practices, I’ll tell you this: embedded images should be your no. 1 choice for most use cases. In other words, if you want your email signature to display as intended, go for local images. At least for standard emails sent directly from email apps.

As I mentioned earlier, you might encounter minor issues when recipients use certain email apps, such as Apple Mail. While the images will be OK when your email is received, they might get broken on replying – either disappear or be restored to their original size and break your signature’s layout. You can fix the first issue by enabling the option to include attachments with replies in the email app settings. You can prevent the second issue by resizing images to the desired dimensions before adding them to a signature. This can be done using any graphics editor, such as Photoshop, Canva, or GIMP.

That doesn’t mean you should write off linked images completely. There are cases in which they might be a better choice.

When to use linked images?

There are at least two scenarios where linked images may be worth considering:

• Newsletters. Almost all newsletters are built on hosted images and for a couple of reasons. Newsletters are usually sent with tools designed for mass-mailing. Since linked images don’t increase email size, they are quicker to send and don’t use up as many “email credits” if your plan is based on size and not volume. Besides, people are used to having their newsletter’s images blocked by default.
• Large size & high-quality graphics. For example, if you want to showcase a large, high-quality image of your latest product in an email, a linked image might be the better choice. Using an embedded image could clog both your and your recipients’ mailboxes faster than you can say “embedded graphics in email signatures” (isn’t that a mouthful!).

However, remember that linked images come with downsides beyond your control, such as issues with spam filters, email security solutions, external hosting services, and so on.

Which email platforms support adding linked and embedded images?

To check if your email platform supports either of the two image adding methods, have a look at the following quick reference table:

How to add a hosted or an embedded image to an email signature?

How to add an image to an email signature? Regardless of the email platform, the following general methods apply:

• Linked images – if your email app supports adding linked images directly from the editor, use the ‘Insert Image’ option, or similar, and provide the image’s web address. In Outlook, it’s a bit trickier since there’s no such option there. The easiest way to add a linked image in such a case is to use an email signature generator and paste the whole signature. One way or another, here’s a useful guide on how to handle those images.
• Embedded images
  • CID images – for email apps that support adding embedded images, click the ‘Insert picture’ option, or similar, and select the image from your local drive. Alternatively, you can copy and paste the image from your local drive into the signature editor in your email app.
  • BASE64 images – this can be tricky because email apps don’t support adding these images directly from their signature editors. To use them, you’ll need some HTML knowledge. Start by converting an image to BASE64 format (there are plenty of online converters available). Then, include the encoded string in the <img> tag’s src attribute, like that:

<img src="{image's BASE64 code}" />

How to control email signature images for the whole company?

Adding images to email signatures can be trickier than expected. Imagine what could happen if you left this task in the hands of every employee in your company… Chaos guaranteed.

If you need to manage email signatures for an entire company and care about your brand image, there’s only one way to do it without going insane – that’s using an email signature management tool, such as CodeTwo Email Signatures 365. Its editor also gives you full control over every aspect of the images used in email signatures:

The tool allows you to enjoy centralized email signature management for everyone in your company, enabling instant organization-wide updates. It also includes useful features like scheduled email signatures, company- and user-specific out-of-office notes, auto-replies, one-click surveys, and more.

If you use Microsoft 365 for business email and wonder if this tool is right for you, start a free 14-day trial now.