The new libewf release now supports writing EWF files using an acquire tool called, ewfacquire. This tool supports reading devices in Linux, FreeBSD, NetBSD, OpenBSD, MacOS-X/Darwin. On other platforms it can convert a raw (dd) image into a EWF file. With the tool you can acquire diskimages just like in Encase or FTK and save the same metadata and hash value within the ewf file.
You can download the sourcecode on the project website: