When I developing SharePoint apps, I prefer to use my custom master page, as the idea is to create responsive design. One of the issues I had was to how to add a logo or an image in the master page. The solution is still classic asp.net control called image.
<asp:Image runat="server" ImageUrl="../../Images/sp_logo.png" />
You can apply style on the image by setting CssClass property of the control, as well as you can use all other properties. See full documentation for this tag here: http:// https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.webcontrols.image?view=netframework-4.7.2
Popescu Andrei Vlad 