Your logo, if it fits the size criteria, can be added to the backend management portal (CAS). It is added to Configuration>Company Details.

It will then be on the WinPOS.

The maximum file size for the logo is 1mb and the size cannot exceed 110 by 110 pixels and in JPG file format.

If you want your logo on the receipts, add it to your store (on cas>management>hierarchy>modify hierarchy - select store). and add the image

If your printer supports it, the Store Logo will be printed on the receipts, the logo should be in a jpeg. format and be no larger than  120 x 120 pixels and 1 mb. The Store Logo will be the image printed on a receipt on the top center. This logo will also appear on the email Receipts to your customers.