For the blind, navigating the digital world can be as tricky as moving through the physical one.

Some companies have tried to make their sites easier for the world's 39 million blind people to use. Facebook, for instance, just introduced a new image-recognition feature that lets blind users "see" photos on the site.

But blind advocates say fixes like Facebook's don't solve the biggest obstacles blind people face online.

"We think it's pretty cool," Mark Riccobono, the president of the National Federation of the Blind, told The Huffington Post. "But we get concerned about flashy technology."

"For the average blind person, it's not whether they know something is in a photo or not that determines whether they can do online banking, pay their bills or buy groceries," said Riccobono, who is blind.

Even as the Internet becomes an increasingly necessary feature of modern life, much of the web is difficult for blind people to use effectively.

A range of technologies exist to help blind people navigate the web. Braille keyboards and text-to-speech programs convert text to audio, which allows blind people to consume information on the web aurally. The devices can also transform speech into text, which allows blind people to "type." These devices often work well with thoughtfully designed websites. But they hit snags when sites have elements that aren't clearly labeled or are incompatible with keyboard shortcuts, which blind people rely on.

"Websites that have been designed from the beginning with accessibility in mind are easy for blind people to use -- they're easy to navigate, you can jump around pretty effectively and get information as effectively as a sighted person," Riccobono said. But, he said, many sites still have "artificial barriers" that make performing basic online tasks difficult for blind users.

One of the biggest barriers is unclear labeling. In order to describe what's on a given webpage, text-to-speech programs comb through the source code for labels that describe the page's elements. They then say those labels aloud. If elements aren't clearly labeled in the source code -- if a checkout button, say, is just labeled "image" -- it can make navigating the page very frustrating for users who rely on spoken descriptions to move around the site.

"If I go on an e-commerce website and put stuff in my cart, but get to the payment screen and have trouble because the checkout button's not labeled -- that's a high degree of frustration," Riccobono said.

Web developers can use accessibility guidelines for blind users when designing their websites. But even when they refer to those guidelines, web companies don't always do a good job implementing them, Riccobono said.

"If you don’t test [your code] for accessibility, and a problem arises and it's not dealt with, then the code gets launched anyway," he said. Once finalized, it can be difficult to retrofit websites to improve accessibility.

We need to do in the digital world the same thing we’ve done in the physical world. Mark Riccobono, National Federation of the Blind

Blind advocates have urged the Obama administration to update the Americans with Disabilities Act to include explicit standards for web accessibility for blind users. While President Barack Obama initially seemed amenable to the standards -- in 2010, he named them among “the most important updates to the ADA since its original enactment” -- last year his administration quietly postponed consideration of new web accessibility standards until 2018.

For Riccobono, updating the ADA is a necessary step toward equal access for the blind.

"We need to do in the digital world the same thing we’ve done in the physical world," he said. "The lack of standards makes it very difficult for businesses to understand when they’ve met a high standard of accessibility."