xterm actually does support ReGIS and Sixel graphics! However, it must be compiled with --enable-regis-graphics` (or `--enable-sixel-graphics`); and it's likel

xterm actually does support ReGIS and Sixel graphics! However, it must be compiled with --enable-regis-graphics` (or `--enable-sixel-graphics`); and it's likely that your distro didn't compile it with those flags. If they did, you can get ReGIS support by running xterm in VT340 mode (`-ti vt340`).