OpenVisaPhoto specs, and where the "photo (back)" information goes
The "back of the photo" still exists; it's just a separate upload.
Each person needs one photo taken by a commercial photographer in the last 12 months. For a digital photo, the studio details that used to go on the back are a separate upload, as Guide 5289 explains in Appendix C.
1. What photo does IRCC want?
Taken within the past 12 months, by a commercial photographer, to the permanent residence photo specifications (size, head position, plain background, neutral expression). Studios that do passport photos know the "Canada PR" spec; ask for it by name.
taken within the past twelve (12) months … taken by a commercial photographer
2. What information has to go "on the back"?
the name and date of birth of the person in the photo; the name and complete address of the photography studio; the date the photo was taken
3. Where does it go when the photo is digital?
For digital photos, the information required for the back of one photograph can be provided as one separate document with a confirmation from the photo studio (e.g. receipt). This document should be uploaded in the Portal section titled "Additional Supporting Documents - Other".
So: the photo file in the photo slot, and the studio's receipt or a signed note with the three items above as a separate PDF under "Other". If you scanned a paper photo instead, upload the front and the back as two images.
4. What about children and infants?
Same spec, same back-of-photo information for each person, including a baby. Studios that do infant passport photos can meet the spec. A phone photo at home doesn't meet the rule: the photo has to be taken by a commercial photographer.
5. On the checklist
Photos are an item on the checklist (IMM 5533 or IMM 5589) for each person in the application. The studio receipt isn't on the checklist, which is why it gets forgotten; add it to your own index.
OpenVisa is software, not a lawyer or RCIC. This page explains what the rules and forms say; it is not advice about your case. You submit your application yourself.