Trust logo is a service for all Comodo certificates except for Multi-domain ones. It is a dynamic site seal which displays certain information about the certificate depending on the validation type.
For DV certificates, for example, PositiveSSL, EssentialSSL, PositiveSSL/EssentialSSL Wildcard, etc., the visitor will see the domain name secured by a seal, the country used in the CSR, and the certificate warranty.
OV and EV certificates will make the logo display the company name, domain URL, physical address used in the CSR, telephone, fax and email contact.
The instructions about trust logo implementation can be found here.
Here you can set up more features of your logo such as its position on the website and trust logo type.
Corner of trust is a service for EV certificates only. The EV corner of trust graphic is sent to your admin contact email together with the certificate files. The instructions about its implementation are similar to the trust logo ones and can be found here.
You can also visit the Comodo help page for more information about the corner of trust.