This is very common issue with wordpress websites. Many times we solved (unable to upload images in wordpress) same issue So we written detailed article on same topic. This is very common issue with linux or windows server or computer. When you do the wordpress setup you need to give the write able permission to your wp-content/uploads folder.
If you got the following error: when you upload the image.
“Screen Shot 2013-01-28 at 13.53.32 PM.png” has failed to upload due to an error: Unable to create directory wp-content/uploads/2013/01. Is its parent directory writable by the server?
if you are using windows then right-click the uploads folder and uncheck the is read checkbox. Change ownership of uploads folder. Change owner to apache.
solved: unable to upload images in wordpress
if you are using the linux then use following command:
chown apache:apache -R wp-content/uploads
If you need to chmod 777 your folder, your hosting company have a wrong setup.