Suggestion: in the image generated in "local to btc", there should be a small line underneath, saying the day/time that the value was updated.
But that doesn't make sense, because every new load makes a printout of the current value.[/quote]
I like the suggestion. Updates can fail for many reason, including browser cache[/quote]
It would only make sense if you kept the page open without refreshing, and that sounds useless.
I do this all the time

The main point of the tool was to quote the value of BTC whenever a page is loaded
Here's another idea: make the price-image an animated GIF. First, show the current price. After 10 minutes, show "price expired" (and keeep that frame for 10 years).