All right, let's see what we've got here:
SCP-XXXX is to be kept in a standard Object Containment Locker.
This doesn't need to be capitalized.
Instances of SCP-XXXX-1 are to be contained in standard Humanoid Anomaly Cells for further testing.
If these instances are created during the testing process, it might be wise to say that earlier on to bridge the sentences talking about testing and this one together, right now it feels a bit disjointed. Additionally, "Humanoid Anomaly Cells" doesn't need to be capitalized, but I'd say something like "standard humanoid containment cell" instead.
SCP-XXXX is a mahogany picture frame, measuring 7.6 by 10.1 dm (30 in x 40 in)
Drop the imperial conversions as they don't really serve a purpose. 7.6 and 10.1 are overly specific, when 8 and 10 could be used in their place. Additionally, this is a rather large picture frame?
One this process is complete
I think you mean, "once".
whichever takes up more space will be the subject SCP-XXXX-1 becomes.
In this case, I don't see how the subjects are the ones in the photographs considering they aren't the ones in the testing environment.
Overall, the idea isn't particularly interesting or original. There are already a lot of scips that transform the person viewing them into something else entirely, here's a list of pages tagged with transfiguration for example, and this one doesn't really add anything new or exciting to the very common trope. This is also extremely bare bones, I realize this isn't the final product, but still there really isn't much there to critique. What is there currently has a very clearly defined mode of function and that's all there is to it, essentially a Generic Magic Object.
What's the story behind this picture frame? Why was it created and by who? Did it fulfill its intended purpose or did something go awry with it? Answering some questions like that within the draft would help with it narrative wise and start to take this beyond the bounds of a "thing that does a thing". If there are to be some sort of testing logs included with this, make the subjects used in your tests characters in your story. What are you trying to convey through this article? What is the reader of this article supposed to feel while reading it? Try to incorporate that, and bear it in mind, when moving forward.
