It's already available but it needs some hours to set up, a variable number of hours to build (my 4 cores i7 takes 6 hours) and about 30Giga of free disk space
If you feel it's too difficult, than probably it is. Still, you may want to give it a try, as it may be easier than you think 
An alternative path is to build just the SDK (or to obtain one from the openwrt website) and adapt instructions like those from fibasile about nodejs, so that you can build a custom version of package gd
Last alternative is to look for a totally different solution: one could be using fswebcam for taking pictures and use another program for changing them adding time and date