You cannot do it by size. A resistor will have a resistance value, regardless of its physical size, and similar sized resistors can have different resistance values. Larger physical sizes usually have to do with the amount of current/wattage they can handle. When they are that small, they aren't always marked. Without a schematic, or an associated device component sheet, the likelihood of determining the actual resistance value will be difficult, unless you remove them from the board.
What you can do, however, is to take a multimeter and check the resistance value across each ends of the resistors. It looks like R20 and R21 are in like size and similar circuit placement, all of them doubled up and being next to the 620's. Note their locations in relation to R84, R86, and R88. See if all of R2X resistance values seem to match up closely. You may get lucky there. You should be able to check the resistance while they are on the board, unless the circuit they are in prevents that. But that is what I would try first.
The 620 resistors can be checked in the same way. You should be able to get a resistance value with a multimeter and they should all be very close, if they are good. If you find abnormally different values, you may have to remove them from the board to check them. In that case, you should be able to determine if they are still holding a similar value to the other ones. If so, there is probably nothing wrong with them.
Why do you think R22 and R23 are bad? I do see a bit of discoloration on the ends on the solder locations and the traces running from them. Resistors do dissipate some heat, and that is normal. It doesn't look like an abnormal or excessive darkening though. Is that why you think there is something wrong?
Your next step would be to take very clear photos of the top and bottom of the entire circuit board, provide us with a description of the problem you are having with the device, and tell us what kind of device you are troubleshooting. That usually helps the most.
