You can pass your business logo in your checkout flow when using PayPal buttons, using one of two methods:

Method 1: Creating or editing a PayPal button.

When creating or editing a button, use the advanced variable option by clicking Customize advanced features (optional), then add the image_url variable in the add advanced variable dialog.

Example: image_url=http://www..../YourLogo.gif

Method 2: Code your logo into your checkout flow using NVP or SOAP.

NVP

Use the LOGOIMG variable to pass your logo image through your custom-coded checkout flow.

Example: &LOGOIMG=https://www.../YourLogo.gif

SOAP

Use the cpp-logo-image variable to pass your logo image through your custom-coded Checkout flow.

Example: https://www.../YourLogo.gif

See also:

Can I customize buttons in Checkout?