What age are you? have you had problems with your foreskin before? The picture is not very good, I take it you are not circumcised?
Swellings like this should subside in a day or two if you abstain from masturbating: so how is this now? …
This is completely normal for circumcised and uncircumcised men. What happens when you masterbate and theres no skin movement you are essentially tearing your skin on the inside and as a result it swells. This frequently happens when you try to masterbate using your skin but have way too little foreskin left over from your circumcision. Sorry buddy
Try not to masterbate as vigorously or cut back as repeated damage like this can lead to serious conditions like priapism or permanent nerve damage/erectile dysfunction. You could try to stretch the skin out using foreskinrestoration.org and seek help there. It’s very safe to do but slow- successful stretching of the skin will alleviate your issues