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a model to build self‐describing
images for assisting screen
reader users
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Topics covered
Web Accessibility
Steganography techniques
Browser Extensions
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Web Accessibility
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(A11y)
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Screen Readers
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Screen Readers
JAWS
NVDA
VoiceOver
Speakup
TalkBack
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Demo
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Excerpt from Accessible images (AIMS): a model to build self‐describing images for assisting screen reader users
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Pros
+ Ease of implementation
+ Works with any image MIME type
+ Supported in browsers since
HTML 2
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Cons
– Requires coding knowledge
– Decoupled from the actual image
– Plenty* of devs have little to no a11y skills
*presenter’s observation of peers from over 12 years of experience in front-end development field
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May 16, 2006 newscientist.com/article/dn9177-gamers-help-the-blind-get-the-picture
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Steganography
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Steganography
the practice of concealing messages
or information within other
nonsecret text or data.
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there are many steganography
techniques and approaches
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+ concealing text in images
+ using LSB method
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1 convert text to bits
2 store bits in LSBs of pixel data
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close up photo of a lion facing to the left
99
1100011
ASCII character code
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20, 255, 102
0010100
LSB
c
99
1100011
ASCII character code
save!
1
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Assumptions
? knowing length of alt text
? method to compute bit position in image
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Knowing the length of alt text
? store length in consistent pixel location
? use special character to indicate end (EOF?)
? NLP (lol no)
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Computing bit position in image
? use a PRNG with seed
? decoder needs to know the seed
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Browser extension
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Browser extension
third party script that can run on
pages loaded by a user
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Browser extension
a terrifying way to give third party
code a same-origin policy waiver
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Implementation
noopkat.github.io/a11y-alt-stego
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Pros
+ Description is portable with image
+ Less code
+ Less effort
+ Rad use of steganography
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Cons
– Single language restriction
– Lossless image format required
– Compression can destroy / corrupt data
– Most significant human labor not removed
– Opt-in, standard adoption challenges
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thanks