Create a new document in Adobe illustrator (Go to File + New or Control-N) and give file name, paper size and bleed if needed and click ok. (Bleed is not necessary for online it will give while printing)
Go to file and select place and choose picture from folder, which you wanted convert from jpg to line art.
(Refer picture A & B)
Select picture from the folder and place it in the document.
Now image will look like this on the artboard.
(Note: If image is colored, convert it in to gray scale or black and white)
Select the image with selection tool (V)
Go to control panel and click over image trace option, now you will get the expand option click it.
Click over the expanded image and ungroup it. Now use selection tool to select individual part of the image as shown below.
Select individual object or together and go to swatches and remove fill by clicking over none, then click over stroke (X) and give outline color.
Line art picture after conversion.
Also, you can fill different colors inside and use it as a solid image.
For more information you can visit https://www.youtube.com/watch?v=hGHP_5uxiSQ or
– Sunitha Biswas