There are two ways to add images to a report: by its path using addLinkedImage (note that in case the file is inside jars you must check if the ReportGenerator you use support adding them with supportImagesOfJarFilesOrURLs function), or by direct sending the image data to the generator, using the function addImage.
    Let's add big centered image from its link. Note that the image is only loaded a single time per report, even if it's used multiple times at it (it's an easy optimization afterwards).

String imgLink = Thread.currentThread().getContextClassLoader().getResource(
                       "nerval.png").getPath();

reportGenerator.setTextAlignment(ReportTextAlignment.CENTER);
reportGenerator.addLinkedImage(imgLink, 661);
         

    The advantage of addImage is that if you use it often on lots of reports, you can load it just a single time per application instance. The other big advantage is that you can dynamically generate your report images and directly add them to the report without the need to save them to a file. For example, if you use generated charts at your reports (by a third party library), you can add them easily that way.
    Let's, for example, generate a QRCode (using the library QRGen) and add it to our report:

byte[] qrImage = QRCode.from("Nerval Reports")
                       .withSize(200, 200)
                       .to(ImageType.PNG).stream().toByteArray();

reportGenerator.addImage(qrImage, "NervalQR", 200);
reportGenerator.beginGroup(ReportGroupType.PARAGRAPH);
reportGenerator.addText("Nerval Reports generated QRCode");
reportGenerator.endGroup();
         

    You can normally use images in your headers and footers. The only thing to note here is to avoid using groups (as the alignment is predefined by header/footer position). Also, if you plan to use TeXReportGenerator, do not use direct added images in headers or footers, as they aren't supported there. Let's see our page header and footer generation function:

String nervalSmallLink = Thread.currentThread().getContextClassLoader()
                               .getResource("nerval_small.png").getPath();

reportGenerator.beginPageHeaderLeft();
reportGenerator.addLinkedImage(nervalSmallLink, 50);
reportGenerator.addSeparatorLine();
reportGenerator.endPageHeaderLeft();

reportGenerator.beginPageHeaderCenter();
reportGenerator.addText("Tutorial 6 - Images");
reportGenerator.endPageHeaderCenter();

reportGenerator.beginPageFooterCenter();
reportGenerator.addCurrentPageNumber();
reportGenerator.endPageFooterCenter();

reportGenerator.beginPageFooterRight();
reportGenerator.addSeparatorLine();
reportGenerator.addLinkedImage(nervalSmallLink, 50);
reportGenerator.endPageFooterRight();
         

    That's it.