Here are a few tips when working with your photos.

When you double click to open your photos it will probably open with Microsoft Office Picture Manager. This program will allow you to rotate your picture, crop your picture, adjust the brightness and contrast, resize and compress your photo.

This is the original photo. It takes up 83.9 KB. This is the photo resized at 50%. The resized one is 23.0 KB .
ocean_adventure.jpg rezied_ocean_adventure_50.jpg

If you are posting the pictures on your webpage or wiki, you will want to compress them so they display faster. When I compressed the picture from the original size it
from 83.9KB to 23.7KB. You can also compress pictures for email so the picture will open quickly for the person receiving the email. When I compressed the picture for email, the file size changed from 83.9KB to 5.36KB.
You always want to make sure that each student in your class has signed the Release of Student Directory Information from the district.
There are two categories Release of Directory Information for School Sponsored Purposes and Release of Directory Information to Third Parties.
Make sure you the students have checked yes on the school sponsored purposes. If a form comes back and does not allow this you may want to send a note home to that parent explaining how you would like to use the pictures on your class wiki.
If they still do not want the photo of the child released you can open the photo in Microsoft Photo Editor and use the smudge tool and lightly make the face where you cannot identify the student.