Are fonts in ImageMagick system dependent, or do they come inside ImageMagick and can be equally used in any platform.
The fonts that are available on a particular system are system-dependent (for example, on Windows you're likely to have many .ttf (TrueType) and .otf (Open TrueType) fonts; on Mac, you're likely to also have PostScript fonts; and on Linux, you'll have X11 fonts).
But some types of fonts can be copied from system to system and will be supported - read on...
You can list all the fonts currently available to Imagemagick with -list font
option (for versions prior to 6.3.6, use 'type' instead of 'font').
Different font types have varying levels of support in operating systems - even if the file itself is not OS-specific, the OS must have support for rendering the font. TTF and OTF are reasonably universally supported now; PostScript (as far as I know) require special tools for Windows and not all applications can use them; and X11 fonts' support is limited to various flavors of Unix.
Even if a font is supported, the way to render it can differ between operating systems and even between different libraries. When Safari 3 for Windows came out, the difference in antialiased rendering between Windows' ClearType and Apple's method was very visible.
Yes, the core fonts are system dependent. However, if ImageMagick was compiled with FreeType support (most versions are) you can then bundle True Type fonts and pass the path to the font file to ImageMagick to use.