计算图像哈希值

    function h = hash(inp,meth) 
    % HASH - Convert an input variable into a message digest using any of 
    %        several common hash algorithms 
    % 
     
    
    inp=inp(:); 
    % convert strings and logicals into uint8 format 
    if ischar(inp) || islogical(inp) 
    inp=uint8(inp); 
    else % convert everything else into uint8 format without loss of data 
    inp=typecast(inp,'uint8'); 
    end 
    
    % verify hash method, with some syntactical forgiveness: 
    meth=upper(meth); 
    switch meth 
    case 'SHA1' 
        meth='SHA-1'; 
    case 'SHA256' 
        meth='SHA-256'; 
    case 'SHA384' 
        meth='SHA-384'; 
    case 'SHA512' 
        meth='SHA-512'; 
    otherwise 
    end 
    algs={'MD2','MD5','SHA-1','SHA-256','SHA-384','SHA-512'}; 
    if isempty(strmatch(meth,algs,'exact')) 
    error(['Hash algorithm must be ' ... 
        'MD2, MD5, SHA-1, SHA-256, SHA-384, or SHA-512']); 
    end 
    
    % create hash 
    x=java.security.MessageDigest.getInstance(meth); 
    x.update(inp); 
    h=typecast(x.digest,'uint8'); 
    h=dec2hex(h)'; 
    if(size(h,1))==1 % remote possibility: all hash bytes  128, so pad: 
    h=[repmat('0',[1 size(h,2)]);h]; 
    end 
    h=lower(h(:)'); 
    
    return