First of all, make sure you are in Edit mode of your dashboard.
Then find the right sidebar, and click on the Add text widget button.

Then, in the Add text widget segment, select Upload and hit Next.

After that, select your image file, and if you wish, you can add a description of your widget.

The next step is to put in your Widget Title, select the widget size, and select the “Regular Card” option from the drop-down menu.

Don't forget to click submit at the end.

NOTE: You can also use markdown for all passive widgets and footers. 

Learn all about text widgets here.