Sometimes, as you’re discovering, it can be very challenging to get a good picture of the stripe between your legs. I would hope your dom appreciates this, and knows you’re trying your best. Don’t feel pressured into doing anything, he needs to understand your real-life constraints.
Panty-pulling can be a way of experimenting with erotic pain when actually spanking yourself isn’t practical. If you can’t attach your panties to a chair, you can try tying them to your bedframe, and lie down under your covers.
If you have a very stretchy pair of panties, and can pull them up to the level of your shoulder blades, you might be able to pass your bra straps through your underwear and clip them together.
Or, if your panties don’t stretch that far, tug them up and loop a belt through the leg holes at the back. Then close the belt so you’re wearing it above your hips, then put on another layer of clothes on top of it so it’s not visible to others. This way you can wear your panties pulled tight underneath your clothes for an extended period of time. The longer they’re tight, the sorer and more obvious your stripe will be.
I’ve written another post with tips on how to take better pictures. Where the top advice is use mirrors to obtain better angles, and use the strongest source of illumination you can find, daylight being by far the best.
Take your time experimenting, and don’t allow yourself to feel pressured by others. Remember, all this is play, if it stops being fun, you should stop completely. You can always start again when your domestic circumstances are more conducive, and you have more privacy.