Limesurvey 3 allows creating so called "Theme options" which allow to easily place logos at predefined positions. You can switch them on and off at the interface and also select the logo to use there. Here is an example of the Limesurvey theme "Backy" we created recently.
This is how it looks like when adding a placeholder logo top left:
Best regards/Beste Grüße,
Dr. Marcel Minke
survey-consulting.com
offlinesurveys.com
Feel free to contact me by email for professional LimeSurvey support!