Identifying different denominations of dollar bills has long been a problem for the sight-impaired in the US. A US$1 bill is the same size and shape as a $100 bill, making them hard to differentiate.
Many use techniques like folding different bills into different shapes, but this doesn't help when receiving change in a store. LookTel now has an app called Money Reader for the iPhone 4/3GS and fourth-generation iPod touch which will check bills and speak their values out loud.
LookTel says its Money Reader can use the iPhone's camera to "read" currency and speak its value aloud in real time, and the app doesn't need an internet connection. It currently recognises $1, $2, $5, $10, $20, $50 and $100 bills, and it costs $2 from the App Store.
The Treasury Department was ordered last year to change US currency to make it easier for the blind and partially-sighted to identify it -- other countries make their notes different sizes and shapes to help with this -- but until then, this could be a big help.