How to use FILE in binary and text mode in C

Question

Even in Binary or Text mode it is working(image,document,...). Then what is the real use of these mode and how to use them.

#include<stdio.h>
#include<stdlib.h>
int main()
{
    FILE *fp;
    unsigned char buffer[756396];  
    fp=fopen("ref.jpg","r");    //rb
    if(fp==NULL)
    {
        printf("File not present");
        exit(0);    
    }
    else
        fread(buffer,sizeof(buffer),1,fp);  
    fclose(fp);
    fp=fopen("ref1.jpg","w");  //wb
    if(fp==NULL)
    {
        printf("File can not be created");
        exit(0);    
    }
    else
        fwrite(buffer,sizeof(buffer),1,fq);
    fclose(fp);
    return 0;
}

output

Above code create a copy of an image

I want to know the real time application of where and when to use them.