Try this :
unzip test.zip '*.jpg'
The argument after the filename is the file to be extracted. See man unzip
Arguments section:
[file(s)] An optional list of archive members to be processed, separated by spaces. (VMS versions compiled with VMSCLI defined must delimit files with commas instead. See -v in OPTIONS below.) Regular expressions (wildcards) may be used to match multiple members; see above. Again, **be sure to quote expressions that would otherwise be expanded** or modified by the operating system.