Hello :
About Video Capture solution,
Basicly,you need a Video decoder to covert Analog Video to Digital Video YCbCr,you can visited Philips web-site SAA7115,SAA7118,SAA7114.....
Then You need a FIFO to store the image (for example Averlogic AL440....) Then you can use a micro control to read from fifo then transfer to RS-232 !
BGS,Jones