PDFs: imagemagick & poppler

I was looking for a way to extract images from pdfs to know the resolution of each embeded image.
poppler has a tool named "pdfimages" to extract images from the pdf, usage:

pdfimages -j file.pdf img

Then, use tools from imagemagick to read characteristics of the images, usage:

display img.jpg

identify -verbose img.jpg

imagemagick let create a pdf file from jpg images, usage:

convert imageA.jpg imageB.jpg file.pdf pdf