Nice! ;o) I love the hands-to-heart image. Yay! Nice, simple photo, and I like how it looks kind of like an old-timey film, with a hint of grain and the rounded rectangle shape.
Not quite sure what *all* the differences are between top and bottom photo -- I see a difference in font color, and the photo on the bottom seems brighter -- that's all I see, tho. (are those the two photos you meant to compare? sometimes there are photo hosting issues.) I think I prefer the brown font color to black, if that's one thing you're choosing between . . . it feels warmer and friendlier to me. Love the light purple with the brown.
I *love* that font, too! It's scripty and looks like "wedding" but it's still modern-looking and informal. AND easy to read! Nice job.

But please, for the love of Pete:
previous posters are correct: replace the "your" with "you're", AND also the "its" with "it's".

(don't be offended, it's a pet peeve.

)
Other *minor* text things you might want to look at again before printing a bajillion of them and sending them out (since I do this sort of designing-and-proofreading thing for a living):
- "21st August 2010" sounds awkward -- to ME (but that's also my part of the world -- from your post you seem to be in England, where dates go in the European order) -- In my neck of the woods, I might write "21st of August," or "August 21st" -- If you're in a British-speaking place, maybe ditch the "st" and have it read "21 August 2010"
BUT, I'm not as familiar with date-writing standards in the not-US. So feel free to ignore me.

- In the last line, if you're going to capitalize the W in "We hope you can join us!" then you need to put a period after "Details are on the back." (Otherwise it looks like you forgot an important part of the sentence about details. And then people might be going, "Details are on the back, and --what? Where? the back of what? What details? NooOOOOOOOO!" Can't have that, can we?)
Hope this is helpful! I love the idea of photo invites, and always a fan of the DIY wedding stuff. Best of luck in your wedding planning etc!