InputStream is = new ByteArrayInputStream(qlist.get(0).getDataImage());
IOUtils.copy(is, response.getOutputStream()); 

<td>
<img src="${el.dataImage}" width="124" height="124" alt=""/>
</td>

src="${el.dataImage}" 

IOUtils.copy(is, response.getOutputStream()); 

//String imageBase64 = Base64.getEncoder().encodeToString(qlist.get(0).getDataImage());
//qlist.get(0).setImageBase64(imageBase64);

<img src="${el.dataImage}" width="124" height="124" alt=""/>

<img src="${el.imageBase64}" width="124" height="124" alt=""/>

src="${el.dataImage}" 

<img th:src="@{/images/{id}(id=${el.idImage})}"/>

@GetMapping("/images/{id}")

    public void showImage(@PathVariable String id, HttpServletResponse response) throws IOException {
        response.setContentType("image/jpeg");
        List<Image> qlist = qservice.imagelist(1, 12);  // (1, 12) - это мои отладочные данные

        InputStream is = new ByteArrayInputStream(qlist.get(Integer.parseInt(id)).getDataImage());
        IOUtils.copy(is, response.getOutputStream());
    }