All we know from this photo is it's a 1U server and what ports are on the back. A standard cabinet/rack is 42U high, this server is 1U, one twice as "thick" would be 2U and so on.
It could have been on rails, there are many ways rails mount and most modern rail kits stay in the cabinet/rack when you pull the server so you aren't fumbling them around, cutting your hands and nailing your groin as you work on it.
We are seeing the bottom of the case, back of the system in this photo, you can't tell if it's toolless or requires a screwdriver to open up from this pic.
You need to look at the front and back of the server. Look at the label your pinky is covering. Sometimes in the lid you remove there is information, but rack mount servers will display information on the front and back of the server so you don't have to remove it from the rack to see what it is.
Look for a system ID or service tag, it's different than serial number. You can look info up on the big sites like HP, Dell, IBM.