Get the compression filter used on an image.
char *pdfGetImageCompression(PDFHandle pdf, int idx)
This function returns the compression filter, if any, used on the idxth image on the page specified in the last call to pdfGetImages. It returns NULL if the image is not compressed.

The compression filter names (as of PDF 1.7) are: LZWDecode, RunLengthDecode, CCITTFaxDecode, DCTDecode (JPEG), FlateDecode, JBIG2Decode, and JPXDecode (JPEG 2000).

char *comp; int nImgs, i; pdfGetImages(pdf, 1); nImgs = pdfGetNumImages(pdf); for (i = 0; i < nImgs; ++i) { comp = pdfGetImageCompression(pdf, idx); printf("image %d: %s compression\n", i, comp); }