How can I create logo for each user I want each user to create their own site-logo. This is not multi-site, this is a single site only. How can I do it?
Add a field to the user profile and use this as a replacement for the logo. Use the page_preprocessor to add the user logo to the page template. Replace the logo by the one the user provided or show a default one. 

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template_preprocess_page
Setting up variables to use in a template