Patch from Debian: "conditionally enable tesseract-related functions", see
https://sources.debian.org/patches/k2pdfopt/2.55%2Bds-2/0007-k2pdfoptlib-k2ocr.c-conditionally-enable-tesseract-r.patch/

Index: k2pdfoptlib/k2ocr.c
--- k2pdfoptlib/k2ocr.c.orig
+++ k2pdfoptlib/k2ocr.c
@@ -41,16 +41,16 @@ typedef struct
     int ni;
     char initstr[256];
     } OCRTESSINITINFO;
-#endif
 static void k2ocr_show_envvar(char *buf,char *color,char *var);
 static void k2ocr_status_line(char *buf,char *color,char *label,char *string);
 static void k2ocr_tesslang_init(char *lang,int assume_yes);
+#endif
 static void k2ocr_ocrwords_add_subregion_to_queue(MASTERINFO *masterinfo,OCRWORDS *words,
                                         BMPREGION *region,K2PDFOPT_SETTINGS *k2settings);
 #endif /* HAVE_OCR_LIB */
 
 /* Functions to support extracting text from PDF using MuPDF lib */
-#ifdef HAVE_MUPDF_LIB
+#if (defined(HAVE_MUPDF_LIB) || defined(HAVE_DJVU_LIB))
 static void k2ocr_ocrwords_get_from_ocrlayer(MASTERINFO *masterinfo,OCRWORDS *words,
                                              BMPREGION *region,K2PDFOPT_SETTINGS *k2settings);
 static int ocrword_map_to_bitmap(OCRWORD *word,MASTERINFO *masterinfo,BMPREGION *region,
@@ -425,6 +425,7 @@ static void *otinit(void *data)
 void k2ocr_showlog(void)
 
     {
+#ifdef HAVE_TESSERACT_LIB
     static char *funcname="k2ocr_showlog";
 
     if (k2ocr_tess_status<0 && k2ocr_logfile!=NULL && wfile_status(k2ocr_logfile)==1
@@ -468,6 +469,7 @@ void k2ocr_showlog(void)
         k2printf(header,divider,"End","\n");
         willus_mem_free((double **)&bigbuf,funcname);
         }
+#endif
     }
             
 
@@ -724,9 +726,13 @@ printf("Done k2ocr_ocrwords_add_subregion_to_queue()\n
 void k2ocr_multithreaded_ocr(OCRWORDS *words,K2PDFOPT_SETTINGS *k2settings)
 
     {
+#ifdef HAVE_TESSERACT_LIB
     ocr_cpu_time_secs += ocrwords_multithreaded_ocr(words,ocrtess_api,maxthreads,
                                                     k2settings->dst_ocr,
                                                     k2settings->ocr_dpi);
+#else
+    printf("k2ocr_multithreaded_ocr(): tesseract unsupported\n");
+#endif
     }
 
 
