You can definitely use it to create static images and such for your site. With Helvetica on your computer, you can create as many images for as many sites as you want.
See this page for further reading. The general idea with fonts is that they're treated like software. So, if you have a computer program on your computer, you can use it to do whatever on your computer but you can't distribute that software. Same idea with fonts; it's on your computer and you can make all kinds of things with it, but if you embed it on a website you're essentially making a copy of the font software and placing it on another server and leaving it available for people to download illegally. Embedding it in apps is typically a no-no too without a special license, because that font is leaving your computer and going somewhere else and being copied hundreds/thousands of times.
But when you make an image, the font software is staying on your computer and the image is just a bunch of pixels. So that's cool.
IANAL and such.