How many hair grafts I need to cover the bald areas on my head? (Photos)

The number of grafts needed will  be determined by what a patients goals may be. Hairline restoration vs. adding density to a thinning crown will necessitate different counts. Addressing both will often times require multiple procedures. 
A good rule of thumb is that 1200-1500 grafts will be needed to restore a receding hairline. 2000 grafts will add reasonable density to an area of the crown about the size of a compact disc. 
Based upon your photos alone, I would venture to guess that you may need ultimately need upwards of 3000+ grafts (split between 2 procedures), if the goal is to restore good density throughout. You may want to consider strip grafting vs. FUE. While FUE will allow you to avoid a linear scar there is a limit to the amount of grafts which can be harvested (10-15%) before one begins to experience thinning at the donor site. This is not a concern in strip grafting where the donor site is excised and all of the follicles in a given area can be harvested (simply put...no bald spot).
As always, discuss your concerns with a board certified plastic surgeon (ABPS) with experience in hair restoration.

Although it is always preferable to consult with a surgeon to asses fully and realistically what can be achieved it seems like you would need to undergo 2 hair transplants in order to cover your balding / thinning areas. 3500-4000 grafts is what would be needed and that would be achieved over 2 sessions with a year break in between both. The reason why 2 sessions is needed is because of how much is permitted to extract from your donor area based on its' density and quality. You never want to over harvest the donor area or you will end up looking like hair is missing.