When I search for my store smartoffice.com.ng on google search, I see the images/logo.png appear as the suffix of the title in some search results. What could possibly be the cause? I have tried removing the link from webmaster tools but it is still there.
Google has a system for picking the title in the search results.
First of all it will check your site/page
<title> tag to see if this covers the page content. Your page title of the example is:
Office Supplies, Stationery, Toners and Inks, Office Equipment/Funiture, School Supplies Graphic Calculators - default
Which does seem to contain a lot of keywords you're hoping to get found on, but doesn't really cover the page content.
So second, Google will check for elements on the page itself, like
<h1> tags. The
<h1> on your pages are the product names and do not contain any "images/logo.png".
So third, Google will see what the text is of the links that are linking to your page. This one is hard to find out, but if you have Google Analytics then you can see what inbound URL's refer to a certain page.
Also see this article about the page title: http://searchenginewatch.com/sew/news/2342232/why-google-changes-your-titles-in-search-results
And I think this article can help you to find all pages that link to that one page through Google Analytics: https://www.distilled.net/blog/miscellaneous/how-to-find-all-the-links-to-that-cool-thing-you-made/