I have a friend who is about the whitest person you could meet and he is technically here illigally. He was born in England and his grandfather kidnapped him and brought him to the US. By the time anything was done England didn't want to take him and the US didn't want to let him work. He is over 21 and has been dealing with paperwork processing since he turned 18.
The process isnt easy. Hes been in this country since the age of 4 and is finding things difficult even with family resources in both places. I can't immagine how hard it would be for a non-english speaking person with no family to help them and no money. I don't think rounding up illigals is the answer and I don't think making the process harder is the answer either. If they can prove their willingness to adopt our language, pass some tests in that regard and find a job then they should be allowed at least part time residency.
There is no way to visually spot an "illigal". They tried that in the late 1800s and it caused a lot of bloodshed and heartache. Id like to think civilization has advanced a bit since then.