Photo applications and websites that create galleries of photos seem to be a dime a dozen; so why is ExpressDigital so successful? 

A key ingrediant is found in Joel’s  MicroISV interview:

Michael:
…If you could pick one tip based on
your experience in going from zero to hero, what would be the thing you
would tell yourself from five years ago if you could give yourself a
piece of advice now to be the one thing not to miss – the one thing you
should do.

Joel: Can I have two things?

Bob: You can have two things.

Joel:
The number one thing is a micro-ISV shouldn’t be one person, it should
be two people at the very least and one of them should have the
business and marketing and sales skills experience.

The second part, and Bob alluded to this earlier, which is my
prototypical example of the photo gallery which is probably nine
million micro-ISVs have made an application where it’s like “Hey,
everybody’s got these digital cameras my application lets you upload
all your pictures and put them on the web and make web galleries.”
There have been about a million of these and a very tiny number of them
have been successful and the vast majority of them have been instant
flops. For some reason this is an incredibly appealing idea for
software developers to do, maybe because they feel like they know how
to do everything, all the steps they’re going to need to do to write
the code to make this work, but for some reason they never really make
it work.

But what I’ve always told these people time and
time again, and they never listen to me, is instead of making the
generic “upload your pictures application” take a very, very small
niche audience – wedding photographers – and make the ultimate
application for wedding photographers. Find out exactly what wedding
photographers need. There’s a lot of money around wedding
photographers, they get paid an awful lot of money, and figure out
exactly what their workflow is. If you need to find wedding
photographers because they’re in the yellow pages and there are
directories of these things. Call them all and find out what they want
and try to sell them your solution.