add more information about how to ignore invalid rotation values in input images

README.md

@@ -82,7 +82,10 @@ Bugs
    only nine different values from 1 to 9 are permitted, Anroid phones and
    Canon DSLR cameras produce JPEG images with the invalid value of zero.
    Either fix your input images with `exiftool` or similar software before
-   passing the JPEG to `img2pdf` or run `img2pdf` with `--rotation=ifvalid`.
+   passing the JPEG to `img2pdf` or run `img2pdf` with `--rotation=ifvalid`
+   (if you run img2pdf from the commandline) or by passing
+   `rotation=img2pdf.Rotation.ifvalid` as an argument to `convert()` when using
+   img2pdf as a library.
 
  - img2pdf uses PIL (or Pillow) to obtain image meta data and to convert the
    input if necessary. To prevent decompression bomb denial of service attacks,
@@ -191,6 +194,10 @@ The package can also be used as a library:
 	with open("name.pdf","wb") as f:
 		f.write(img2pdf.convert(glob.glob("/path/to/*.jpg")))
 
+	# ignore invalid rotation values in the input images
+	with open("name.pdf","wb") as f:
+		f.write(img2pdf.convert('test.jpg'), rotation=img2pdf.Rotation.ifvalid)
+
 	# writing to file descriptor
 	with open("name.pdf","wb") as f1, open("test.jpg") as f2:
 		img2pdf.convert(f2, outputstream=f1)

src/img2pdf.py

@@ -1277,17 +1277,25 @@ def get_imgmetadata(
                     elif value in (2, 4, 5, 7):
                         if rotreq == Rotation.ifvalid:
                             logger.warning(
-                                "Unsupported flipped rotation mode (%d)", value
+                                "Unsupported flipped rotation mode (%d): use "
+                                "--rotation=ifvalid or "
+                                "rotation=img2pdf.Rotation.ifvalid to ignore",
+                                value,
                             )
                         else:
                             raise ExifOrientationError(
-                                "Unsupported flipped rotation mode (%d)" % value
+                                "Unsupported flipped rotation mode (%d): use "
+                                "--rotation=ifvalid or "
+                                "rotation=img2pdf.Rotation.ifvalid to ignore" % value
                             )
                     else:
                         if rotreq == Rotation.ifvalid:
                             logger.warning("Invalid rotation (%d)", value)
                         else:
-                            raise ExifOrientationError("Invalid rotation (%d)" % value)
+                            raise ExifOrientationError(
+                                "Invalid rotation (%d): use --rotation=ifvalid "
+                                "or rotation=img2pdf.Rotation.ifvalid to ignore" % value
+                            )
     elif rotreq in (Rotation.none, Rotation["0"]):
         rotation = 0
     elif rotreq == Rotation["90"]: