1 picture 2"x2" required for US Passport.

Retailers:

Walgreens $15.99 + tax

CVS $16.99 + tax

Walmart - doesn't do passport pictures but you can print yours for $7.44

Online Options:

Price per digital copy / price per 2 printed pictures with delivery:

makepassportphoto.com - $2.99 /  n/a

easypassportphotos.com - $5.95 / $9.45

ivisa.com - $5.95 / $9.45

photoaid.com - $6.95 / $9.95

123passportphoto.com - $6.98 / n/a

idphotodiy.com - $6.98 / n/a

passportphotos.com    - n/a / $14.50

passport-photo.online   - $13.95 / $16.95

idphoto4you.com - free digital photo, but doesn't remove background.

epassportphoto.com - free digital photo, but doesn't remove background.

online-passport-photo.com - do not recommend (doesn't remove background, changes photo proportions).

persofoto.com - do not recommend (doesn't remove background, changes photo proportions).