Alternate Text For Image

Hi All,

Can anybody tell how to put alternate text to images using the combination of Span tag and Alt tag(eg /Span <</Alt (alternate text for image)>> BDC image object.. EMC)(feature mentioned on page 812 under "10.8.2 Alternate Descriptions" topic in PDF Reference(Version 1.5 onwards)).
I know about the logical structure using which we can have alternate text for images. I wanted to know how to have alternate text for images using the second option mentioned in Alternate Descriptions of pdf spec.

I have tried the following but I am unable to get the alternate text for image in pdf using Span and Alt tag....
%PDF-1.5
%âãÏÓ
1 0 obj<</Producer()/CreationDate()>>
endobj
2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>
endobj
3 0 obj<</Type/Page/Parent 2 0 R/MediaBox[0 0 200 300]/ArtBox[0 0 200 300]/Contents 5 0 R/Resources<</ProcSet[/PDF/ImageC/ImageI/ImageB/Text]/XObject<</X0 6 0 R>>>>>>
endobj
4 0 obj<</Type/Catalog/Pages 2 0 R/OpenAction[3 0 R/Fit]>>
endobj
5 0 obj<</Length 91>>stream
b /Span<</Alt(alternate text for image)>>
b BDC
b q
b 26.32 0 0 9.8 80 210.2 cm
b /X0 Do
b Q
b EMC
endstream
endobj
6 0 obj<</Type/XObject/Subtype/Image/Width 188/Height 70/BitsPerComponent 8/ColorSpace/DeviceRGB/Filter[/DCTDecode]/Length 20028>>stream
%binary image data endstream
endobj
xref
0 7
0000000000 65535 f
0000000015 00000 n
0000000103 00000 n
0000000153 00000 n
0000000327 00000 n
0000000393 00000 n
0000000529 00000 n
trailer
<</Size 8/Root 4 0 R/Info 1 0 R/ID[<494e4431313937353335353536383433><494e4431313937353335353536383 433>]>>
startxref
20711
%%EOF

Thanks,
Arvind.