How to know if you’re being watched?

Can anyone tell me what this is?

I think my phone is being watched, but I’m not tech savvy and need help.

i know people use hidden spy apps through WiFi and I have found fuzzy pictures that I know is me, but can’t prove until I can clear them up better.

ive used picture apps, but need more help learning about spy devices used to watch a person. Please help !!