Flash CMS is very hard to deal with, you can build your own using Flex, but it is very difficult to maintain.
the only one i've ever used is: Flash CMS, CMS for Flash, Flash Based CMS and that was an amazing peice of kit, but you need to have a ActionScript or Flex coder to do all the maintainance and a PHP coder too.
It just came to mind as I was thinking about it the other day. I do have a client coming up soon that I may need to use it for. But I think he has basic knowledge of Photoshop and I'm sure he is smart enough to edit text into the right place(xml document).
I would like to try out using a fcms. But the price is a lot to 'try'!
What I think I would predominantly be using it for would be updating images and correlating text. You can control the size of the dynamic text box via actionscript. But I haven't found out how to control the size of the images. The only way I have found is sizing the images to an agreed size and then calling them in via xml.
I would not focus on controlling the size of the images client-side. When I code anything "admin" or "cms" that includes an image I usually handle the rest server side.
All these websites you see with a huge collection of products didnt require the admin user to size the product images right before uploading them to the website. If it did m it would be very badly coded.
To accomplish what you need the only question I had was: How does flash upload files to a server? and on my first search in google the first link was this;
It sort-of confirmed my theory about needing another layer, so I went on to click the "continue reading" link... if you go to page two (skipping the flash stuff) you can see that they use 2 simple lines of PHP to handle moving this image;