Java fast image comparing -

hi formatted phone , uploaded photos pc, when wanted add photos phone saw have multiple duplicates of images. wanted merge photos 1 folder upload phone wrote java code.

public class main {  public static int imgctr = 1; public static file dest = new file("d:\\finalfinal");  public static void main(string[] args) throws exception {     getcontent("d:\\restorefinal");     getcontent("d:\\restore1");     getcontent("d:\\restore2"); }  public static string getextension(string filename) {     string extension = "";      int = filename.lastindexof('.');     if (i > 0) {         extension = filename.substring(i + 1);     }     return extension; }  public static boolean isimage(string extension) {     if (extension.equalsignorecase("jpg") || extension.equalsignorecase("jpeg")             || extension.equalsignorecase("png"))         return true;     return false; }  public static boolean compareimages(file a, file b) throws exception {     fileinputstream fisa = new fileinputstream(a);     fileinputstream fisb = new fileinputstream(b);     byte contenta[] = new byte[(int) a.length()];     byte contentb[] = new byte[(int) b.length()];     fisa.read(contenta);     fisb.read(contentb);     string stra = new string(contenta);     string strb = new string(contentb);     fisa.close();     fisb.close();     return stra.equals(strb); }  public static void getcontent(string path) throws exception {     file source = new file(path);     arraylist<file> content = new arraylist<file>(arrays.aslist(source.listfiles()));     while (!content.isempty()) {         file f = content.get(0);         if (isimage(getextension(f.getname()))) {             if (dest.listfiles().length == 0) {                 path p = paths.get(dest + "\\i" + imgctr + "." + getextension(f.getname()));                 imgctr++;                 files.move(f.topath(), p);                 system.out.println(imgctr);             } else {                 file[] alreadythere = dest.listfiles();                 boolean match = false;                 (file cmp : alreadythere) {                     if (compareimages(f, cmp)) {                         match = true;                         break;                     }                 }                 if (!match) {                     path p = paths.get(dest + "\\i" + imgctr + "." + getextension(f.getname()));                     imgctr++;                     files.move(f.topath(), p);                     system.out.println(imgctr);                 }             }         }         content.remove(0);     } } 

}

i wrote image compare string compares because pixel comparing took long (had around 2k photos). problem somehow copies photo multiple times without difference can see. , searched source folders copies photos arbitrarily, photos didn't have duplicates had duplicates in destination folder. doubt compare method, couldn't find mistake.

so can me find fault or suggest fast , more reliable way compare images?

comparing pixels fine if images haven't been resaved or haven't passed through lossy file format such jpeg. if haven't start off checksum comparison , if checksums don't more extensive pixel comparison, though lossy algorithms require different approach.