Confluence uses the Lucene search engine, which indexes all content including attachments. This means image names, along with the names of any other attachments, will appear in the search results. You can minimally configure the search, but not to the point where you can prevent attachments being displayed in the results.
However, on the Search page there are filters on the left hand side, which you can use to filter the results by type:
Search Type Filters.png
So you can filter the results to just show Pages, for example.
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