Selecting 'yes' values from checkbox in query

I have a table with Photo ID, title, etc and whether or not we have a hardcopy of the photo. The hardcopy field is defined as a check box with Yes/No values.
I would like to run a query that only selects the photos for which we have hardcopies and then return a number of fields (title, caption, date).
When putting together the query, I can't seem to build the correct expression that will select only those records that have the hardcopy field check box showing 'Yes'.
I have the Photos table showing in the top half of the query window, and for the criteria for the Hardcopy? field in the bottom half of the window have tried the expression [Photos]![Hardcopy?]="Yes".
I get an error message "Data type mismatch in criteria expression" when I try and run this.
Thanks for the help.

Try is "True" or "-1" (without quotes)
S-

Thanks for that. Both True and Yes work - I was just putting them into the criteria box enclosed in quotes!!!