All you have to do is a print screen (Using the "Prt Scrn/Sys Rq" button on most computers), then ctrl-V to paste into your Inkscape document and delete the pasted screenshot strait away!
Then go and find the folder where you have saved the document and your screenshot will be in that folder, named something like "pastedpic_MMDDYYYY_HHMMSS.png" where MMDDYYY are the date (in month-day-year format), and HHMMSS is the time of pasting (in hour-minute-second format).
Useful until you get a thousand pictures with random names all over your computer, but when you know about it it can be quite handy
