Since Image Gallery was merged with Document Library (in 6.1 I guess), now every image added through web content article is a regular file in Document Library. This among others causes, that the image is indexed and searchable, which in most cases is not desirable and does not make sense.
Above that, each web content article could be marked as "not searchable" (article.isIndexable() == false). Then the JournalArticleIndexer ignores such article, but the images in that article are still indexed using DLFileEntryIndexer.
Solution could be to add indexable property (true/false) for DL file entry and DL folder entities. Then editors could e.g. place web content images in dedicated, not indexed folder or adjust the indexable property on per image basis. Then also when web content article is marked as not indexed, the referenced images could be set and not indexed.