I have made a custom field in inventory section i want to transfer its value in sale invoice line, i have created another custom field here with same name so whenever i select that item i want that custome value to come also
You don’t need a custom field in the invoice lines. Instead in the custom field edit page check the box that says “Show custom field on printed documents”
No.
I have an image custom field in inventorty page so images are showing there of inventory items. I want that images to come in sale invoices as well so for that i have created a custom field in sale invoice - line with title “picture”. now what i want is the picture code to be fetched from the inventory custom field to this sale invoice - line of the selected item.
That’s not how it works.
Delete the custom field for Invoice -- line item and then go back to your custom field for Inventory items and do this 
No way to fetch that picture in sales invoice. Just enable the print option of custom field that will show up on invoice template. this can show up in sales invoices page too.