Knowledge Base

How to avoid problems with base64 images


You use base64 images in your client-side (Outlook) signature. Unfortunately, you find these images broken, or your signature cannot be added to emails in Outlook or Outlook on the web (OWA) due to the following error: 

Your signature could not be inserted. Try again. If the problem persists, contact your organization’s administrator.


Base64 encoding allows you to turn different types of data (images included) into a readable string. Then, the string can be embedded directly into your code (e.g. the HTML code of your signature). The main advantage of such an approach is that the data doesn’t have to be fetched from external resources because it’s already there – in the code. However, the same can be achieved using embedded images.

Essentially, base64-encoded images are technically supported in both client-side and server-side signature modes (you can insert them manually into your HTML code), although they can cause unexpected errors or behaviors. Note that email clients’ rendering capabilities are much worse than those of actual web browsers. That’s why, the best idea is to embed your images when designing a template in the editor available in CodeTwo Email Signatures for Office 365 – this method has been proved to work on various platforms and with number of different email clients. To embed a traditional PNG or JPEG (JPG) image in your signature template, simply click the Picture button on the editor’s ribbon, select the Embedded picture option, and choose your picture file (Fig. 1.).

Adding an embedded picture to your email signature.
Fig. 1. Adding an embedded picture to your email signature.

With images embedded that way, you both avoid issues related to using base64 encoding, and your recipients no longer need click any ‘download pictures’ (or similar) button.

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