Using BackgroundImage in RDLC report, image is rendering with 96dpi. Most report are design to be printed and most printer is 300dpi.

Image should be able to have render 300dpi.

See : https://social.technet.microsoft.com/Forums/sqlserver/en-US/48de91f9-1844-40c1-9614-5ead0b4b69a5/sql-server-reporting-services-faq?forum=sqlreportingservices#P1Q14 (Part I / Q 14)