Golf me an ASCII Alphabet
Python 3, 375 bytes
f=lambda i:&quot;\n\n&quot;.join(&quot;\n&quot;.join(map(&quot; &quot;.join,zip(*[[x.replace(&quot;0&quot;,&quot; &quot;)[a*5:a*5+5]for a in range(5)]for x in[[&quot;{:025b}&quot;.format(int(c,36))for c in'0 JPCFL J2UKE 92Y3Y J2KAM JOMCF JOMC0 92B72 AYP81 JFM3J JFMHO AZC7M AB6ZJ B5I5T B43N5 92YWE J2UJ4 92YY7 J2UQC 926UM JFM2S AYE5Q AY8G4 AYHKH AT6Q9 AT6KK AWU7'.split()][x!=&quot; &quot;and ord(x)-64]for x in j.upper()]])))for j in i.split(&quot;\n&quot;))

See this code running on ideone.com. 
The same code, but somehow nicely indented, formatted and commented:
f = lambda i: \

    # join multiline strings together using an empty line as separator:
    &quot;\n\n&quot;.join(

        # join the string lines of one big output line together: 
        &quot;\n&quot;.join(

            # join the corresponding rows of the letters together using &quot; &quot;:
            map(&quot; &quot;.join, zip(*

                # make a list (output line) of list (output characters) 
                # of strings (single character's rows):
                [

                    # replace 0s with spaces and split the bit strings into
                    # chunks of 5 characters - the rows of each letter:
                    [x.replace(&quot;0&quot;, &quot; &quot;)[a*5 : a*5+5] for a in range(5)]

                    for x in [

                        # split the space separated character codes and
                        # convert them from base 36 to 
                        # base 2 strings of length 25:
                        [&quot;{:025b}&quot;.format(int(c, 36)) for c in

                         # the encoded font data (reformatted):
                         '0 JPCFL J2UKE 92Y3Y J2KAM JOMCF JOMC0 92B72 '
                         'AYP81 JFM3J JFMHO AZC7M AB6ZJ B5I5T B43N5 92YWE '
                         'J2UJ4 92YY7 J2UQC 926UM JFM2S AYE5Q AY8G4 AYHKH '
                         'AT6Q9 AT6KK AWU7'.split()]

                        # select element 0 if we want a space, else find
                        # out the index from the ASCII code of the letter:
                        [x != &quot; &quot; and ord(x) - 64] 

                        # repeat for every character in the input line:
                        for x in j.upper()
                    ]
                ]
            ))

        # repeat for every line in the input
        ) for j in i.split(&quot;\n&quot;)
    )

I also decided to go for base 36 encoding as that's the highest base Python's built-in int() natively supports. Here is a short Python 3 script I wrote (ungolfed) that converts font definitions like in the question into base 36 codes: My converter on ideone.com
The result consists of the character 1 as enabled pixel and a space   as disabled pixel. Here's a single example run:
Input (line break as \n):
Hello World
Python rocks

Output:
1   1 11111 1     1      111        1   1  111  1111  1     1111 
1   1 1     1     1     1   1       1   1 1   1 1   1 1     1   1
11111 1111  1     1     1   1       1 1 1 1   1 1111  1     1   1
1   1 1     1     1     1   1       11 11 1   1 11    1     1   1
1   1 11111 11111 11111  111        1   1  111  1 1   11111 1111 

1111  1   1 11111 1   1  111  1   1       1111   111   111  1   1  111 
1   1  1 1    1   1   1 1   1 11  1       1   1 1   1 1   1 1  1  1    
1111    1     1   11111 1   1 1 1 1       1111  1   1 1     111    111 
1       1     1   1   1 1   1 1  11       11    1   1 1   1 1 1       1
1       1     1   1   1  111  1   1       1 1    111   111  1  1   111