pdfimages -j test.pdf test && for file in $(find . -name "test*.jpg"); do identify "$file"; done

./test-000.jpg JPEG 2500x1961 2500x1961+0+0 8-bit DirectClass 1.022MB 0.000u 0:00.000

$ pdfimages -list example.pdf
page   num  type   width height color comp bpc  enc interp  object ID x-ppi y-ppi size ratio
--------------------------------------------------------------------------------------------
   1     0 image    2244  2244  cmyk    4   8  image  no       215  0   301   301  418K 2.1%
   2     1 image     900   600  rgb     3   8  image  no       324  0  1524  1525 35.5K 2.2%

Image: test-0000.jpg
Format: JPEG (Joint Photographic Experts Group JFIF format)
Mime type: image/jpeg
Class: DirectClass
Geometry: 6600x5100+0+0
Resolution: 600x600
Print size: 11x8.5

Format: PDF (Portable Document Format)
Mime type: application/pdf
Class: DirectClass
Geometry: 792x612+0+0
Resolution: 72x72
Print size: 11x8.5

5100/8.5=600
6600/11.0=600