This happens with email signatures that store their elements on your computer instead of online cloud. For example, Google suite (Gmail) email servers store everything online and that is why images in emails and signatures are always visible (they are already on internet). These signatures you can just copy/paste from your email signature to Salestrekker and they will work:
On the other hand, desktop mail clients (Outlook, Mac Mail app, Mozilla Thunderbird etc.) tend to store content of their emails and messages locally - on your computer. This causes issues because files are not on the internet and can't be located and displayed when you copy/paste signature to Salestrekker:
How To in 7 steps:
1. Extract images from desktop mail client by saving them in specific folder
2. Upload all of your images from signature to online server: Imgur (its free and you can easily create account). Right click on uploaded image and open it in new tab. Copy url address and paste it signature (step 4. image 2).
4. Using online HTML visual editors (or simply is composing email in Gmail as in example bellow) - copy and paste initial signature as a whole, then remove broken links and add new images from URL
5. Do this for all images.
6. Once signature is set, just copy paste it from editor (or Gmail new message compose box) to Salestrekker in Settings > My Account
7. Your signature is ready:
It will work now because all images are located on internet and will be loaded from there.