@Override
    protected List<PackagePart> getMainDocumentParts() throws TikaException {
        List<PackagePart> parts = new ArrayList<>();
        for (PackagePart part : sheetParts) {
            // Add the sheet
            parts.add(part);

            // If it has drawings, return those too
            try {
                for (PackageRelationship rel : part
                        .getRelationshipsByType(XSSFRelation.DRAWINGS.getRelation())) {
                    if (rel.getTargetMode() == TargetMode.INTERNAL) {
                        PackagePartName relName =
                                PackagingURIHelper.createPartName(rel.getTargetURI());
                        parts.add(rel.getPackage().getPart(relName));
                    }
                }
                for (PackageRelationship rel : part
                        .getRelationshipsByType(XSSFRelation.VML_DRAWINGS.getRelation())) {
                    if (rel.getTargetMode() == TargetMode.INTERNAL) {
                        PackagePartName relName =
                                PackagingURIHelper.createPartName(rel.getTargetURI());
                        parts.add(rel.getPackage().getPart(relName));
                    }
                }
            } catch (InvalidFormatException e) {
                throw new TikaException("Broken OOXML file", e);
            }
        }

        //add main document so that macros can be extracted
        //by AbstractOOXMLExtractor
        parts.addAll(extractor.getPackage()
                .getPartsByRelationshipType(PackageRelationshipTypes.CORE_DOCUMENT));

        return parts;
    }
In Excel files, sheets have things embedded in them,
and sheet drawings which have the images
tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-microsoft-module/src/main/java/org/apache/tika/parser/microsoft/ooxml/XSSFExcelExtractorDecorator.java